Podcast
Questions and Answers
Which of the following is the correct compound angle identity for $\cos(\alpha + \beta)$?
Which of the following is the correct compound angle identity for $\cos(\alpha + \beta)$?
- $\cos \alpha \cos \beta + \sin \alpha \sin \beta$
- $\sin \alpha \cos \beta - \cos \alpha \sin \beta$
- $\cos \alpha \cos \beta - \sin \alpha \sin \beta$ (correct)
- $\sin \alpha \cos \beta + \cos \alpha \sin \beta$
The derivation of the compound angle formula for $\cos(\alpha - \beta)$ utilizes which of the following mathematical tools?
The derivation of the compound angle formula for $\cos(\alpha - \beta)$ utilizes which of the following mathematical tools?
- Pythagorean theorem only
- Distance formula and the cosine rule (correct)
- Sine rule only
- Tangent function and sine rule
Given that $\cos(-\beta) = \cos \beta$ and $\sin(-\beta) = -\sin \beta$, which compound angle formula is directly derived using these identities?
Given that $\cos(-\beta) = \cos \beta$ and $\sin(-\beta) = -\sin \beta$, which compound angle formula is directly derived using these identities?
- $\sin(\alpha - \beta)$
- $\cos(\alpha + \beta)$ (correct)
- $\sin(\alpha + \beta)$
- $\cos(\alpha - \beta)$
To derive the formula for $\sin(\alpha - \beta)$, which co-function identity is used in conjunction with the cosine compound angle formula?
To derive the formula for $\sin(\alpha - \beta)$, which co-function identity is used in conjunction with the cosine compound angle formula?
Which of the following is a correct double angle formula for $\cos(2\alpha)$?
Which of the following is a correct double angle formula for $\cos(2\alpha)$?
Using the sum formula for sine, $\sin(\alpha + \beta) = \sin \alpha \cos \beta + \cos \alpha \sin \beta$, how is the double angle formula for $\sin(2\alpha)$ derived?
Using the sum formula for sine, $\sin(\alpha + \beta) = \sin \alpha \cos \beta + \cos \alpha \sin \beta$, how is the double angle formula for $\sin(2\alpha)$ derived?
Given the Pythagorean identity $\sin^2 \alpha + \cos^2 \alpha = 1$, which of the following is a valid alternative form of the double angle formula $\cos(2\alpha) = \cos^2 \alpha - \sin^2 \alpha$?
Given the Pythagorean identity $\sin^2 \alpha + \cos^2 \alpha = 1$, which of the following is a valid alternative form of the double angle formula $\cos(2\alpha) = \cos^2 \alpha - \sin^2 \alpha$?
Which of the following represents the double angle formula for $\sin(2\alpha)$?
Which of the following represents the double angle formula for $\sin(2\alpha)$?
When solving trigonometric equations, what is the purpose of using the CAST diagram?
When solving trigonometric equations, what is the purpose of using the CAST diagram?
What is the general solution for $\tan \theta = x$, where $k$ is an integer?
What is the general solution for $\tan \theta = x$, where $k$ is an integer?
When solving $\sin \theta = x$, why are there generally two sets of solutions, $\theta = \sin^{-1} x + k \cdot 360^\circ$ and $\theta = 180^\circ - \sin^{-1} x + k \cdot 360^\circ$?
When solving $\sin \theta = x$, why are there generally two sets of solutions, $\theta = \sin^{-1} x + k \cdot 360^\circ$ and $\theta = 180^\circ - \sin^{-1} x + k \cdot 360^\circ$?
In the context of solving trigonometric equations, what does 'k' represent in the general solutions?
In the context of solving trigonometric equations, what does 'k' represent in the general solutions?
Which rule is most appropriate for finding the area of a triangle when no perpendicular height is given?
Which rule is most appropriate for finding the area of a triangle when no perpendicular height is given?
Under what conditions is the Cosine Rule most suitable for solving a triangle?
Under what conditions is the Cosine Rule most suitable for solving a triangle?
When should the Sine Rule be applied to solve a triangle?
When should the Sine Rule be applied to solve a triangle?
Given a triangle ABC, where $a$, $b$, and $c$ are the sides opposite angles $A$, $B$, and $C$ respectively, which equation correctly represents the Cosine Rule for finding side $a$?
Given a triangle ABC, where $a$, $b$, and $c$ are the sides opposite angles $A$, $B$, and $C$ respectively, which equation correctly represents the Cosine Rule for finding side $a$?
To find the height ($h$) of a pole $TF$ with base $F$, observed from points $A$ and $B$ at a distance $d$ apart, which of the following correctly applies the Sine Rule in $\triangle FAB$ and the Tangent Ratio in $\triangle TFB$?
To find the height ($h$) of a pole $TF$ with base $F$, observed from points $A$ and $B$ at a distance $d$ apart, which of the following correctly applies the Sine Rule in $\triangle FAB$ and the Tangent Ratio in $\triangle TFB$?
Given $BC = b$, $\angle DBA = \alpha$, $\angle DBC = \beta$, and $\angle DCB = \theta$, how would you correctly express the height $h$ of building $AD$?
Given $BC = b$, $\angle DBA = \alpha$, $\angle DBC = \beta$, and $\angle DCB = \theta$, how would you correctly express the height $h$ of building $AD$?
A surveyor needs to determine the height of a remote mountain. From a point A, the angle of elevation to the peak is $\alpha$. The surveyor then moves a distance $d$ to point B, where the angle of elevation is $\beta$. Assuming the points A, B, and the base of the mountain are collinear, and given that $\alpha < \beta$, what additional information would be MOST crucial to accurately calculate the mountain's height using trigonometric principles?
A surveyor needs to determine the height of a remote mountain. From a point A, the angle of elevation to the peak is $\alpha$. The surveyor then moves a distance $d$ to point B, where the angle of elevation is $\beta$. Assuming the points A, B, and the base of the mountain are collinear, and given that $\alpha < \beta$, what additional information would be MOST crucial to accurately calculate the mountain's height using trigonometric principles?
Consider two observers, Alice and Bob, attempting to measure the height of a cloud directly overhead. Alice is at location A, and Bob is at location B, a known distance $d$ apart. Alice measures the angle of elevation to the cloud as $\alpha$, but due to faulty equipment, Bob's angle of elevation measurement, $\beta$, is unreliable and potentially significantly skewed. Instead, Bob accurately measures the angle $\gamma$ formed at point B between the line of sight to the cloud and the line AB connecting their positions. Given that $\alpha$, $\gamma$, and $d$ are known with high precision, which trigonometric approach would yield the MOST accurate determination of the cloud's height, minimizing the impact of Bob's potentially flawed elevation angle ($\beta$) measurement given only $\alpha$, $\gamma$, and $d$?
Consider two observers, Alice and Bob, attempting to measure the height of a cloud directly overhead. Alice is at location A, and Bob is at location B, a known distance $d$ apart. Alice measures the angle of elevation to the cloud as $\alpha$, but due to faulty equipment, Bob's angle of elevation measurement, $\beta$, is unreliable and potentially significantly skewed. Instead, Bob accurately measures the angle $\gamma$ formed at point B between the line of sight to the cloud and the line AB connecting their positions. Given that $\alpha$, $\gamma$, and $d$ are known with high precision, which trigonometric approach would yield the MOST accurate determination of the cloud's height, minimizing the impact of Bob's potentially flawed elevation angle ($\beta$) measurement given only $\alpha$, $\gamma$, and $d$?
How does deriving general solutions for trigonometric equations account for the periodic nature of trigonometric functions?
How does deriving general solutions for trigonometric equations account for the periodic nature of trigonometric functions?
Which of the following expressions is equivalent to $\cos(\alpha - \beta)$?
Which of the following expressions is equivalent to $\cos(\alpha - \beta)$?
To derive the compound angle formula for $\cos(\alpha + \beta)$ from $\cos(\alpha - \beta)$, which trigonometric identity is primarily used?
To derive the compound angle formula for $\cos(\alpha + \beta)$ from $\cos(\alpha - \beta)$, which trigonometric identity is primarily used?
Which identity is used to transform $\cos(90^\circ - \alpha)$ into $\sin \alpha$ when deriving the compound angle formula for $\sin(\alpha - \beta)$?
Which identity is used to transform $\cos(90^\circ - \alpha)$ into $\sin \alpha$ when deriving the compound angle formula for $\sin(\alpha - \beta)$?
Starting from the compound angle formula for $\cos(\alpha + \beta)$, and knowing that $\cos(2\alpha) = \cos(\alpha + \alpha)$, which of the following is the initial expression for $\cos(2\alpha)$ before simplification?
Starting from the compound angle formula for $\cos(\alpha + \beta)$, and knowing that $\cos(2\alpha) = \cos(\alpha + \alpha)$, which of the following is the initial expression for $\cos(2\alpha)$ before simplification?
Given $\cos(2\alpha) = \cos^2 \alpha - \sin^2 \alpha$ and the Pythagorean identity $\sin^2 \alpha + \cos^2 \alpha = 1$, which of the following is a derived form of $\cos(2\alpha)$ that eliminates $\sin^2 \alpha$?
Given $\cos(2\alpha) = \cos^2 \alpha - \sin^2 \alpha$ and the Pythagorean identity $\sin^2 \alpha + \cos^2 \alpha = 1$, which of the following is a derived form of $\cos(2\alpha)$ that eliminates $\sin^2 \alpha$?
Which of the following is the double angle formula for $\sin(2\alpha)$?
Which of the following is the double angle formula for $\sin(2\alpha)$?
If $\sin \theta = 0.5$, what are the two principal solutions for $\theta$ in the range $[0^\circ, 360^\circ)$?
If $\sin \theta = 0.5$, what are the two principal solutions for $\theta$ in the range $[0^\circ, 360^\circ)$?
For the equation $\cos \theta = x$, the general solutions are given by $\theta = \cos^{-1} x + k \cdot 360^\circ$ and another set of solutions. What is the other set of general solutions?
For the equation $\cos \theta = x$, the general solutions are given by $\theta = \cos^{-1} x + k \cdot 360^\circ$ and another set of solutions. What is the other set of general solutions?
What is the period of the tangent function, which influences the general solution for $\tan \theta = x$?
What is the period of the tangent function, which influences the general solution for $\tan \theta = x$?
When solving trigonometric equations, the CAST diagram is used to determine:
When solving trigonometric equations, the CAST diagram is used to determine:
Which rule is most appropriate to calculate the area of a triangle when you are given two sides and the included angle?
Which rule is most appropriate to calculate the area of a triangle when you are given two sides and the included angle?
In triangle ABC, if you are given all three sides (a, b, c), which rule should you use to find the angles?
In triangle ABC, if you are given all three sides (a, b, c), which rule should you use to find the angles?
When is the Sine Rule applicable for solving a triangle?
When is the Sine Rule applicable for solving a triangle?
Given a triangle ABC, and sides a, b, c opposite to angles A, B, C respectively, which formula represents the Cosine Rule to find angle A?
Given a triangle ABC, and sides a, b, c opposite to angles A, B, C respectively, which formula represents the Cosine Rule to find angle A?
In a 3D problem to find the height of a pole, if you have the distance between two observation points and angles of elevation, which trigonometric rule is initially applied in the horizontal triangle formed by the observation points and the base of the pole?
In a 3D problem to find the height of a pole, if you have the distance between two observation points and angles of elevation, which trigonometric rule is initially applied in the horizontal triangle formed by the observation points and the base of the pole?
To calculate the height $h$ of a building $AD$, given $BC = b$, $\angle DBA = \alpha$, $\angle DBC = \beta$, and $\angle DCB = \theta$, the height is expressed as $h = \frac{b \sin \alpha \sin \theta}{\sin(\beta + \theta)}$. Which trigonometric rule is used in $\triangle BCD$ to find $BD$ in terms of given angles and side $BC$?
To calculate the height $h$ of a building $AD$, given $BC = b$, $\angle DBA = \alpha$, $\angle DBC = \beta$, and $\angle DCB = \theta$, the height is expressed as $h = \frac{b \sin \alpha \sin \theta}{\sin(\beta + \theta)}$. Which trigonometric rule is used in $\triangle BCD$ to find $BD$ in terms of given angles and side $BC$?
Consider the derivation of $\sin(\alpha - \beta)$. Which sequence of trigonometric transformations is applied?
Consider the derivation of $\sin(\alpha - \beta)$. Which sequence of trigonometric transformations is applied?
In the derivation of $\cos(\alpha - \beta)$ using the distance formula, the expression $KL^2 = 2 - 2\cos(\alpha - \beta)$ is equated to which of the following based on coordinate geometry?
In the derivation of $\cos(\alpha - \beta)$ using the distance formula, the expression $KL^2 = 2 - 2\cos(\alpha - \beta)$ is equated to which of the following based on coordinate geometry?
Given the general solution for $\sin \theta = x$ is $\theta = \sin^{-1} x + k \cdot 360^\circ$ or $\theta = 180^\circ - \sin^{-1} x + k \cdot 360^\circ$, what does the term $k \cdot 360^\circ$ represent in these solutions?
Given the general solution for $\sin \theta = x$ is $\theta = \sin^{-1} x + k \cdot 360^\circ$ or $\theta = 180^\circ - \sin^{-1} x + k \cdot 360^\circ$, what does the term $k \cdot 360^\circ$ represent in these solutions?
Why does the general solution for $\tan \theta = x$ only require adding multiples of $180^\circ$ (i.e., $\theta = \tan^{-1} x + k \cdot 180^\circ$), whereas for $\sin \theta = x$ and $\cos \theta = x$, multiples of $360^\circ$ are added?
Why does the general solution for $\tan \theta = x$ only require adding multiples of $180^\circ$ (i.e., $\theta = \tan^{-1} x + k \cdot 180^\circ$), whereas for $\sin \theta = x$ and $\cos \theta = x$, multiples of $360^\circ$ are added?
A surveyor measures the angle of elevation to the top of a mountain from two different points. To accurately calculate the mountain's height using trigonometry, what is the most critical assumption regarding the two points of observation and the mountain?
A surveyor measures the angle of elevation to the top of a mountain from two different points. To accurately calculate the mountain's height using trigonometry, what is the most critical assumption regarding the two points of observation and the mountain?
When solving a 3D trigonometry problem involving heights and distances, why is it often beneficial to first solve for a length in a horizontal triangle before calculating the vertical height?
When solving a 3D trigonometry problem involving heights and distances, why is it often beneficial to first solve for a length in a horizontal triangle before calculating the vertical height?
In the context of deriving trigonometric identities, what general mathematical principle underlies the manipulation and transformation of trigonometric expressions?
In the context of deriving trigonometric identities, what general mathematical principle underlies the manipulation and transformation of trigonometric expressions?
Consider using the double angle formula for $\cos(2\alpha) = 1 - 2\sin^2 \alpha$. In what situation might this form be particularly advantageous compared to $\cos(2\alpha) = \cos^2 \alpha - \sin^2 \alpha$ or $\cos(2\alpha) = 2\cos^2 \alpha - 1$?
Consider using the double angle formula for $\cos(2\alpha) = 1 - 2\sin^2 \alpha$. In what situation might this form be particularly advantageous compared to $\cos(2\alpha) = \cos^2 \alpha - \sin^2 \alpha$ or $\cos(2\alpha) = 2\cos^2 \alpha - 1$?
Which of the following equations correctly represents the compound angle identity for $\sin(\alpha + \beta)$?
Which of the following equations correctly represents the compound angle identity for $\sin(\alpha + \beta)$?
When deriving the compound angle formula for $\cos(\alpha + \beta)$ from $\cos(\alpha - \beta)$, what trigonometric property is utilized?
When deriving the compound angle formula for $\cos(\alpha + \beta)$ from $\cos(\alpha - \beta)$, what trigonometric property is utilized?
Which of the following co-function identities is used to derive the $\sin(\alpha - \beta)$ formula from a cosine compound angle formula?
Which of the following co-function identities is used to derive the $\sin(\alpha - \beta)$ formula from a cosine compound angle formula?
Given the compound angle formula for $\cos(\alpha + \beta)$, which of the following is the initial step to derive the double angle formula for $\cos(2\alpha)$?
Given the compound angle formula for $\cos(\alpha + \beta)$, which of the following is the initial step to derive the double angle formula for $\cos(2\alpha)$?
Starting with $\cos(2\alpha) = \cos^2 \alpha - \sin^2 \alpha$ and using the Pythagorean identity, derive an equivalent expression for $\cos(2\alpha)$ that only involves $\cos^2 \alpha$.
Starting with $\cos(2\alpha) = \cos^2 \alpha - \sin^2 \alpha$ and using the Pythagorean identity, derive an equivalent expression for $\cos(2\alpha)$ that only involves $\cos^2 \alpha$.
What is the simplified form of $\sin(\alpha + \alpha)$ using the sine compound angle formula?
What is the simplified form of $\sin(\alpha + \alpha)$ using the sine compound angle formula?
Given $\sin \theta = -0.5$, which quadrants would contain the angles that satisfy this condition within the range of $0^\circ$ to $360^\circ$?
Given $\sin \theta = -0.5$, which quadrants would contain the angles that satisfy this condition within the range of $0^\circ$ to $360^\circ$?
If $\cos \theta = -\frac{\sqrt{3}}{2}$, what are the general solutions for $\theta$?
If $\cos \theta = -\frac{\sqrt{3}}{2}$, what are the general solutions for $\theta$?
For the general solution of $\tan \theta = 1$, why is the period multiplied by $k$ equal to $180^\circ$ rather than $360^\circ$?
For the general solution of $\tan \theta = 1$, why is the period multiplied by $k$ equal to $180^\circ$ rather than $360^\circ$?
In solving trigonometric equations, what primary role does the CAST diagram serve?
In solving trigonometric equations, what primary role does the CAST diagram serve?
When no height is given, which rule is best used to determine a triangle's area?
When no height is given, which rule is best used to determine a triangle's area?
You are given all three sides of a triangle and need to find the measure of one of the angles. Which rule is most appropriate for this task?
You are given all three sides of a triangle and need to find the measure of one of the angles. Which rule is most appropriate for this task?
Given two sides and a non-included angle of a triangle, which rule should be applied to solve the triangle?
Given two sides and a non-included angle of a triangle, which rule should be applied to solve the triangle?
For triangle $ABC$, which equation correctly represents the Cosine Rule to find angle $A$, given sides $a$, $b$, and $c$?
For triangle $ABC$, which equation correctly represents the Cosine Rule to find angle $A$, given sides $a$, $b$, and $c$?
When dealing with 3D problems involving a vertical pole and observations from two points on the ground, which trigonometric relationship is primarily used in the vertical triangle formed by the pole and the distance to the observation point?
When dealing with 3D problems involving a vertical pole and observations from two points on the ground, which trigonometric relationship is primarily used in the vertical triangle formed by the pole and the distance to the observation point?
In a scenario where you are trying to find the height $h$ of a building $AD$, and you have $BC = b$, $\angle DBA = \alpha$, $\angle DBC = \beta$, and $\angle DCB = \theta$, which trigonometric principle is applied in $\triangle BCD$ to express $BD$ in terms of the given sides and angles?
In a scenario where you are trying to find the height $h$ of a building $AD$, and you have $BC = b$, $\angle DBA = \alpha$, $\angle DBC = \beta$, and $\angle DCB = \theta$, which trigonometric principle is applied in $\triangle BCD$ to express $BD$ in terms of the given sides and angles?
Which of the following sequences of transformations correctly describes the derivation of the formula for $\sin(\alpha - \beta)$?
Which of the following sequences of transformations correctly describes the derivation of the formula for $\sin(\alpha - \beta)$?
In the derivation of $\cos(\alpha - \beta)$ using the distance formula in coordinate geometry, the expression $KL^2 = 2 - 2\cos(\alpha - \beta)$ is equated to which of the following?
In the derivation of $\cos(\alpha - \beta)$ using the distance formula in coordinate geometry, the expression $KL^2 = 2 - 2\cos(\alpha - \beta)$ is equated to which of the following?
What does the term $k \cdot 360^\circ$ represent in the general solutions for $\sin \theta = x$ and $\cos \theta = x$?
What does the term $k \cdot 360^\circ$ represent in the general solutions for $\sin \theta = x$ and $\cos \theta = x$?
A surveyor is tasked with determining the height of a tall building. They measure the angle of elevation from two points on the ground. What essential assumption must they make to accurately apply trigonometric principles in this scenario?
A surveyor is tasked with determining the height of a tall building. They measure the angle of elevation from two points on the ground. What essential assumption must they make to accurately apply trigonometric principles in this scenario?
While trying to determine the height of a cliff using angles of elevation from two land-based observation points, a surveyor finds that one measurement was imprecise. He only has one accurate angle of elevation ($\alpha$), the direct distance ($d$) between the points $A$ and $B$, and the angle ($\gamma$) formed at point B between the line of sight of the cliff and the line $AB$. How can he find the height?
While trying to determine the height of a cliff using angles of elevation from two land-based observation points, a surveyor finds that one measurement was imprecise. He only has one accurate angle of elevation ($\alpha$), the direct distance ($d$) between the points $A$ and $B$, and the angle ($\gamma$) formed at point B between the line of sight of the cliff and the line $AB$. How can he find the height?
What is the primary reason that solving for a length in a horizontal triangle is strategically advantageous before calculating vertical height in many 3D trigonometry problems?
What is the primary reason that solving for a length in a horizontal triangle is strategically advantageous before calculating vertical height in many 3D trigonometry problems?
Suppose you need to solve a complex trigonometric equation involving $\cos(2\alpha)$, and you know the value of $\sin \alpha$. Which form of the double angle formula for $\cos(2\alpha)$ would be most efficient to use?
Suppose you need to solve a complex trigonometric equation involving $\cos(2\alpha)$, and you know the value of $\sin \alpha$. Which form of the double angle formula for $\cos(2\alpha)$ would be most efficient to use?
You are tasked with determining the angle at which a beam of light must be directed from point $A$ to illuminate a solar panel at point $B$. The coordinates of $A$ are $(x_1, y_1, z_1)$, and the coordinates of $B$ are $(x_2, y_2, z_2)$ in a three-dimensional space. There are obstructions that make direct measurement impossible, and the angles must be calculated through trigonometry with the aid of intermediate reference points. Identify the MOST critical factor to ensure an accurate calculation of the required angles.
You are tasked with determining the angle at which a beam of light must be directed from point $A$ to illuminate a solar panel at point $B$. The coordinates of $A$ are $(x_1, y_1, z_1)$, and the coordinates of $B$ are $(x_2, y_2, z_2)$ in a three-dimensional space. There are obstructions that make direct measurement impossible, and the angles must be calculated through trigonometry with the aid of intermediate reference points. Identify the MOST critical factor to ensure an accurate calculation of the required angles.
Flashcards
$\cos(\alpha - \beta)$ Formula
$\cos(\alpha - \beta)$ Formula
States that $\cos(\alpha - \beta) = \cos \alpha \cos \beta + \sin \alpha \sin \beta$.
$\cos(\alpha + \beta)$ Formula
$\cos(\alpha + \beta)$ Formula
States that $\cos(\alpha + \beta) = \cos \alpha \cos \beta - \sin \alpha \sin \beta$.
$\sin(\alpha - \beta)$ Formula
$\sin(\alpha - \beta)$ Formula
States that $\sin(\alpha - \beta) = \sin \alpha \cos \beta - \cos \alpha \sin \beta$.
$\sin(\alpha + \beta)$ Formula
$\sin(\alpha + \beta)$ Formula
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$\sin(2\alpha)$ Formula
$\sin(2\alpha)$ Formula
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$\cos(2\alpha)$ Formula (Form 1)
$\cos(2\alpha)$ Formula (Form 1)
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$\cos(2\alpha)$ Formula (Form 2)
$\cos(2\alpha)$ Formula (Form 2)
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$\cos(2\alpha)$ Formula (Form 3)
$\cos(2\alpha)$ Formula (Form 3)
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General Solution
General Solution
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General Solution Method
General Solution Method
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General Solution for $\sin \theta = x$
General Solution for $\sin \theta = x$
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General Solution for $\cos \theta = x$
General Solution for $\cos \theta = x$
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General Solution for $\tan \theta = x$
General Solution for $\tan \theta = x$
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Area Rule
Area Rule
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Sine Rule
Sine Rule
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Cosine Rule
Cosine Rule
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General Approach to 3D Problems
General Approach to 3D Problems
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Height of a Pole Formula
Height of a Pole Formula
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Height of a Building Formula
Height of a Building Formula
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When to use the Cosine Rule
When to use the Cosine Rule
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When to use the Sine Rule
When to use the Sine Rule
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Cosine Negative Angle Identity
Cosine Negative Angle Identity
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Sine Negative Angle Identity
Sine Negative Angle Identity
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Solving Trigonometric Equations
Solving Trigonometric Equations
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When to use the Area Rule
When to use the Area Rule
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Double Angle Formulas Utility
Double Angle Formulas Utility
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Compound Angle Identities
Compound Angle Identities
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Study Notes
Compound Angle Identities
- The cosine of the difference of two angles: $\cos(\alpha - \beta) = \cos \alpha \cos \beta + \sin \alpha \sin \beta$
- The cosine of the sum of two angles: $\cos(\alpha + \beta) = \cos \alpha \cos \beta - \sin \alpha \sin \beta$
- The sine of the difference of two angles: $\sin(\alpha - \beta) = \sin \alpha \cos \beta - \cos \alpha \sin \beta$
- The sine of the sum of two angles: $\sin(\alpha + \beta) = \sin \alpha \cos \beta + \cos \alpha \sin \beta$
Derivation of $\cos(\alpha - \beta)$
- Using the distance formula and cosine rule: $KL^2 = (\cos \alpha - \cos \beta)^2 + (\sin \alpha - \sin \beta)^2$
- Simplifies to: $KL^2 = 2 - 2 \cos(\alpha - \beta)$
- Equating both expressions gives: $2 - 2 \cos(\alpha - \beta) = 2 - 2 (\cos \alpha \cos \beta + \sin \alpha \sin \beta)$
- Therefore: $\cos(\alpha - \beta) = \cos \alpha \cos \beta + \sin \alpha \sin \beta$
Derivation of $\cos(\alpha + \beta)$
- Using the negative angle identity: $\cos(\alpha + \beta) = \cos(\alpha - (-\beta))$
- Expanding this gives: $\cos \alpha \cos(-\beta) + \sin \alpha \sin(-\beta)$
- Since $\cos(-\beta) = \cos \beta$ and $\sin(-\beta) = -\sin \beta$: $\cos(\alpha + \beta) = \cos \alpha \cos \beta - \sin \alpha \sin \beta$
Derivation of $\sin(\alpha - \beta)$ and $\sin(\alpha + \beta)$
- $\sin(\alpha - \beta)$ can be derived using co-functions: $\sin(\alpha - \beta) = \cos(90^\circ - (\alpha - \beta))$
- Which simplifies to: $ \cos((90^\circ - \alpha) + \beta)$
- Expanding the cosine sum gives: $\cos(90^\circ - \alpha) \cos \beta - \sin(90^\circ - \alpha) \sin \beta$
- Since $\cos(90^\circ - \alpha) = \sin \alpha$ and $\sin(90^\circ - \alpha) = \cos \alpha$, it follows that: $\sin(\alpha - \beta) = \sin \alpha \cos \beta - \cos \alpha \sin \beta$
- Similarly: $\sin(\alpha + \beta) = \sin \alpha \cos \beta + \cos \alpha \sin \beta$
Summary of Compound Angle Formulas
- $\cos(\alpha - \beta) = \cos \alpha \cos \beta + \sin \alpha \sin \beta$
- $\cos(\alpha + \beta) = \cos \alpha \cos \beta - \sin \alpha \sin \beta$
- $\sin(\alpha - \beta) = \sin \alpha \cos \beta - \cos \alpha \sin \beta$
- $\sin(\alpha + \beta) = \sin \alpha \cos \beta + \cos \alpha \sin \beta$
Double Angle Formulas
- $\sin(2\alpha) = 2 \sin \alpha \cos \alpha$
- $\cos(2\alpha) = \cos^2 \alpha - \sin^2 \alpha$
- $\cos(2\alpha) = 2\cos^2 \alpha - 1$
- $\cos(2\alpha) = 1 - 2\sin^2 \alpha$
Sine of Double Angle
- $\sin(2\alpha) = 2 \sin \alpha \cos \alpha$
Cosine of Double Angle
- $\cos(2\alpha) = \cos^2 \alpha - \sin^2 \alpha$
- $\cos(2\alpha) = 1 - 2 \sin^2 \alpha$
- $\cos(2\alpha) = 2 \cos^2 \alpha - 1$
Derivation of $\sin(2\alpha)$
- Starting with the sum formula for sine: $\sin(\alpha + \beta) = \sin \alpha \cos \beta + \cos \alpha \sin \beta$
- Let $\alpha = \beta$, then: $\sin(2\alpha) = \sin(\alpha + \alpha) = \sin \alpha \cos \alpha + \cos \alpha \sin \alpha$
- Therefore: $\sin(2\alpha) = 2 \sin \alpha \cos \alpha$
Derivation of $\cos(2\alpha)$
- Starting with the sum formula for cosine: $\cos(\alpha + \beta) = \cos \alpha \cos \beta - \sin \alpha \sin \beta$
- Let $\alpha = \beta$, then: $\cos(2\alpha) = \cos(\alpha + \alpha) = \cos \alpha \cos \alpha - \sin \alpha \sin \alpha$
- Thus: $\cos(2\alpha) = \cos^2 \alpha - \sin^2 \alpha$
Form 1 for cosine
- $\cos(2\alpha) = \cos^2 \alpha - \sin^2 \alpha$
Form 2 for cosine
- $\cos(2\alpha) = \cos^2 \alpha - (1 - \cos^2 \alpha)$
- $\cos(2\alpha) = 2 \cos^2 \alpha - 1$
Form 3 for cosine
- $\cos(2\alpha) = (1 - \sin^2 \alpha) - \sin^2 \alpha$
- $\cos(2\alpha) = 1 - 2 \sin^2 \alpha$
Solving Trigonometric Equations
- Due to periodicity, trigonometric equations have infinite solutions.
General Solution Method
- Simplify the equation using algebra and trig identities.
- Determine the reference angle using positive values.
- Use CAST diagram to identify quadrants where the function is positive or negative.
- Find angles within a specified interval by adding or subtracting multiples of the period.
- Express angles in the interval $[0^\circ, 360^\circ]$ which satisfy the equation, and add multiples of the period.
- Verify the solutions with a calculator.
General Solutions for Common Equations
- If $\sin \theta = x$: $\theta = \sin^{-1} x + k \cdot 360^\circ$ or $\theta = 180^\circ - \sin^{-1} x + k \cdot 360^\circ$
- If $\cos \theta = x$: $\theta = \cos^{-1} x + k \cdot 360^\circ$ or $\theta = 360^\circ - \cos^{-1} x + k \cdot 360^\circ$
- If $\tan \theta = x$: $\theta = \tan^{-1} x + k \cdot 180^\circ$, where $k \in \mathbb{Z}$ (integers).
Area Rule
- Area of $\triangle ABC$: $\frac{1}{2}bc \sin A = \frac{1}{2}ac \sin B = \frac{1}{2}ab \sin C$
Sine Rule
- $\frac{\sin A}{a} = \frac{\sin B}{b} = \frac{\sin C}{c}$
Cosine Rule
- $a^2 = b^2 + c^2 - 2bc \cos A$
- $b^2 = a^2 + c^2 - 2ac \cos B$
- $c^2 = a^2 + b^2 - 2ab \cos C$
How to Determine Which Rule to Use:
- Area Rule: when no perpendicular height is given.
- Sine Rule: when no right angle is given, and either two sides and an angle (not the included angle) or two angles and a side are given.
- Cosine Rule: when no right angle is given, and either two sides and the included angle or three sides are given.
Using the Cosine Rule
- $b^2 = a^2 + c^2 - 2ac \cos B$
Using the Sine Rule
- $\frac{\sin C}{c} = \frac{\sin B}{b}$
Calculating the Area of a Triangle
- Area of $\triangle ABC = \frac{1}{2}ac \sin B$
General Approach to 3-Dimensional Problems
- Draw a Sketch to visualize the problem.
- Consider the Given Information by identifying relevant triangles and link sides or angles.
- Apply Appropriate Rules like Sine Rule, Cosine Rule, or trigonometric identities as needed.
- Calculate the Desired Quantities, such as lengths, angles, or areas.
Height of a Pole
- Given: $AB = d$, $\angle FBA = \theta$, $\angle FAB = \alpha$, $\angle FBT = \beta$, $\angle TFB = 90^\circ$
- Using the Sine Rule in $\triangle FAB$: $\frac{FB}{\sin \alpha} = \frac{AB}{\sin(180^\circ - \beta)}$
- $FB = \frac{d \sin \alpha}{\sin \beta}$
- Using the Tangent Ratio in $\triangle TFB$: $\tan \beta = \frac{h}{FB}$
- $h = FB \tan \beta = \frac{d \sin \alpha}{\sin \beta} \tan \beta$
Height of a Building
- Given: $BC = b$, $\angle DBA = \alpha$, $\angle DBC = \beta$, $\angle DCB = \theta$
- Using the Sine Rule in $\triangle BCD$: $\frac{BD}{\sin \theta} = \frac{BC}{\sin(\beta + \theta)}$
- $BD = \frac{b \sin \theta}{\sin(\beta + \theta)}$
- Using the Sine Rule in $\triangle ABD$: $\sin \alpha = \frac{h}{BD}$
- $h = BD \sin \alpha = \frac{b \sin \alpha \sin \theta}{\sin(\beta + \theta)}$
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