Unit Circle: Trigonometry Basics

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Questions and Answers

An angle in standard position has its vertex at the origin and its initial side along which axis?

  • Positive x-axis (correct)
  • Negative x-axis
  • Negative y-axis
  • Positive y-axis

If the terminal side of an angle $\theta$ in standard position passes through the point $(\frac{\sqrt{2}}{2}, \frac{\sqrt{2}}{2})$ on the unit circle, what is the value of $\tan(\theta)$?

  • 1 (correct)
  • $\frac{\sqrt{2}}{2}$
  • 0
  • $\sqrt{2}$

Which of the following statements is true regarding the sine function in Quadrant II?

  • Sine is zero.
  • Sine is negative.
  • Sine is positive. (correct)
  • Sine is undefined.

Given that $\sin(\theta) = \frac{1}{2}$ and $\theta$ is in Quadrant II, what is the value of $\cos(\theta)$?

<p>$-\frac{\sqrt{3}}{2}$ (A)</p>
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What is the reference angle for an angle of $240$ degrees?

<p>60 degrees (B)</p>
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Which of the following trigonometric functions is an even function?

<p>Cosine (C)</p>
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If $\cot(\theta) = -1$ and $\sin(\theta) > 0$, in which quadrant does $\theta$ lie?

<p>Quadrant II (B)</p>
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What is the value of $\sec(\frac{\pi}{3})$?

<p>2 (C)</p>
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Which of the following identities is derived directly from the Pythagorean identity?

<p>$1 + \cot^2(\theta) = \csc^2(\theta)$ (D)</p>
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What is the period of the tangent function?

<p>$\pi$ (D)</p>
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What are the coordinates of the point on the unit circle corresponding to an angle of $\frac{3\pi}{2}$ radians?

<p>(0, -1) (A)</p>
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If $\sin(\theta) = 0$, which of the following could be a possible value for $\theta$ (in radians)?

<p>$\pi$ (D)</p>
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Given $\tan(\theta) = \frac{\sin(\theta)}{\cos(\theta)}$, at which point on the unit circle is $\tan(\theta)$ undefined?

<p>(0, 1) (A)</p>
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If the radius of a circle centered at the origin is 10, and a point on the circle corresponds to an angle $\theta$, what are the coordinates of that point in terms of $\theta$?

<p>$(10\cos(\theta), 10\sin(\theta))$ (B)</p>
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Which of the following describes the relationship between $\sin(\theta)$ and $\sin(-\theta)$?

<p>$\sin(-\theta) = -\sin(\theta)$ (C)</p>
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If $\cos(\theta) = -1$, what is the value of $\sin(\theta)$?

<p>0 (D)</p>
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For what values of $\theta$ in the interval $[0, 2\pi)$ is $\csc(\theta)$ undefined?

<p>0 and $\pi$ (B)</p>
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Given that $\sin(\theta) = \frac{\sqrt{2}}{2}$ and $\cos(\theta) = -\frac{\sqrt{2}}{2}$, find the value of $\theta$ in the interval $[0, 2\pi)$.

<p>$\frac{3\pi}{4}$ (D)</p>
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If an angle $\theta$ is in standard position and its terminal side passes through the point $(\frac{1}{2}, -\frac{\sqrt{3}}{2})$ on the unit circle, what is the value of $\theta$ in degrees?

<p>300° (D)</p>
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Flashcards

Trigonometry

Study of relationships between triangle sides/angles.

Unit Circle

A circle with a radius of 1, centered at (0, 0).

Radians

A way to measure angles; a full rotation is 2Ï€.

Standard Position (Angle)

Vertex at origin, initial side on positive x-axis.

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cos(θ)

x-coordinate on the unit circle for angle θ.

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sin(θ)

y-coordinate on the unit circle for angle θ.

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tan(θ)

sin(θ) / cos(θ), slope from origin to (x, y).

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csc(θ)

Reciprocal of sine: 1 / sin(θ).

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sec(θ)

Reciprocal of cosine: 1 / cos(θ).

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cot(θ)

Reciprocal of tangent: cos(θ) / sin(θ).

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0 degrees (0 radians)

sin(0) = 0, cos(0) = 1

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30 degrees (Ï€/6 radians)

sin(π/6) = 1/2, cos(π/6) = √3/2

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45 degrees (Ï€/4 radians)

sin(π/4) = √2/2, cos(π/4) = √2/2

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60 degrees (Ï€/3 radians)

sin(π/3) = √3/2, cos(π/3) = 1/2

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90 degrees (Ï€/2 radians)

sin(Ï€/2) = 1, cos(Ï€/2) = 0

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Quadrantal Angles

Angles on the axes: 0, 90, 180, 270, 360.

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Pythagorean Identity

sin²(θ) + cos²(θ) = 1

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Cosine (Even Function)

cos(-θ) = cos(θ)

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Sine (Odd Function)

sin(-θ) = -sin(θ)

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Periodicity of Sine & Cosine

sin(θ + 2π) = sin(θ); cos(θ + 2π) = cos(θ)

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Study Notes

  • Trigonometry is the study of the relationships between the sides and angles of triangles
  • It's a fundamental branch of mathematics with applications in various fields like physics, engineering, and navigation
  • The unit circle provides a visual and intuitive way to understand trigonometric functions
  • It is a circle with a radius of one unit centered at the origin (0, 0) in the Cartesian coordinate system

Key Concepts

  • Angle Measurement: Angles are measured in degrees or radians
  • A full rotation around the circle is 360 degrees or 2Ï€ radians
  • Important conversions: 180 degrees = Ï€ radians; 1 degree = Ï€/180 radians; 1 radian = 180/Ï€ degrees
  • Standard Position: An angle is in standard position when its vertex is at the origin and its initial side is along the positive x-axis
  • Terminal Side: The side where the angle terminates after rotation

Coordinates on the Unit Circle

  • For any point (x, y) on the unit circle corresponding to an angle θ:
  • x = cos(θ)
  • y = sin(θ)
  • These relationships define the cosine and sine functions for all real numbers θ
  • The coordinates (x, y) represent the cosine and sine of the angle θ, respectively

Trigonometric Functions

  • Sine (sin θ): The y-coordinate of the point on the unit circle
  • Cosine (cos θ): The x-coordinate of the point on the unit circle
  • Tangent (tan θ): Defined as sin(θ) / cos(θ), which is y/x
  • It represents the slope of the line from the origin to the point (x, y) on the unit circle
  • Cosecant (csc θ): The reciprocal of sine, csc(θ) = 1 / sin(θ)
  • Secant (sec θ): The reciprocal of cosine, sec(θ) = 1 / cos(θ)
  • Cotangent (cot θ): The reciprocal of tangent, cot(θ) = cos(θ) / sin(θ) = x/y

Key Angles and Values

  • 0 degrees (0 radians): (1, 0)
    • sin(0) = 0, cos(0) = 1, tan(0) = 0
  • 30 degrees (Ï€/6 radians): (√3/2, 1/2)
    • sin(Ï€/6) = 1/2, cos(Ï€/6) = √3/2, tan(Ï€/6) = 1/√3 = √3/3
  • 45 degrees (Ï€/4 radians): (√2/2, √2/2)
    • sin(Ï€/4) = √2/2, cos(Ï€/4) = √2/2, tan(Ï€/4) = 1
  • 60 degrees (Ï€/3 radians): (1/2, √3/2)
    • sin(Ï€/3) = √3/2, cos(Ï€/3) = 1/2, tan(Ï€/3) = √3
  • 90 degrees (Ï€/2 radians): (0, 1)
    • sin(Ï€/2) = 1, cos(Ï€/2) = 0, tan(Ï€/2) = undefined

Quadrantal Angles

  • Quadrantal angles are angles that lie on the axes (0, 90, 180, 270, 360 degrees)
  • 0 degrees (0 radians): Point (1, 0)
  • 90 degrees (Ï€/2 radians): Point (0, 1)
  • 180 degrees (Ï€ radians): Point (-1, 0)
  • 270 degrees (3Ï€/2 radians): Point (0, -1)
  • 360 degrees (2Ï€ radians): Point (1, 0)

Signs of Trigonometric Functions by Quadrant

  • Quadrant I (0 < θ < 90°): All trigonometric functions are positive
  • Quadrant II (90° < θ < 180°): Sine (sin θ) is positive; cosine and tangent are negative
  • Quadrant III (180° < θ < 270°): Tangent (tan θ) is positive; sine and cosine are negative
  • Quadrant IV (270° < θ < 360°): Cosine (cos θ) is positive; sine and tangent are negative

Trigonometric Identities

  • Pythagorean Identity: sin²(θ) + cos²(θ) = 1
  • Derived Identities:
    • 1 + tan²(θ) = sec²(θ)
    • 1 + cot²(θ) = csc²(θ)
  • Reciprocal Identities:
    • csc(θ) = 1/sin(θ)
    • sec(θ) = 1/cos(θ)
    • cot(θ) = 1/tan(θ)
  • Quotient Identities:
    • tan(θ) = sin(θ)/cos(θ)
    • cot(θ) = cos(θ)/sin(θ)

Even and Odd Functions

  • Cosine is an even function: cos(-θ) = cos(θ)
  • Sine is an odd function: sin(-θ) = -sin(θ)
  • Tangent is an odd function: tan(-θ) = -tan(θ)

Periodic Properties

  • Sine and cosine are periodic with a period of 2Ï€:
    • sin(θ + 2Ï€) = sin(θ)
    • cos(θ + 2Ï€) = cos(θ)
  • Tangent is periodic with a period of Ï€: tan(θ + Ï€) = tan(θ)

Applications

  • Solving Triangles: Finding unknown angles and sides of triangles
  • Navigation: Determining direction and distance
  • Physics: Analyzing oscillatory motion, waves
  • Engineering: Designing structures, circuits

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