Use the diagram shown to solve for the missing parts of the triangle. Round your answer to the tenths.
Understand the Problem
The question is asking to use the Law of Cosines to find the missing parts of a triangle given certain sides and one angle. The problem involves calculations based on the provided dimensions and angle to determine the unknown sides and angles.
Answer
Side \( QS \approx 30.7 \), Angle \( R \approx 74.1^\circ \), Angle \( S \approx 50.9^\circ \)
Answer for screen readers
The missing parts of the triangle are approximately:
- Side ( QS \approx 30.7 )
- Angle ( R \approx 74.1^\circ )
- Angle ( S \approx 50.9^\circ )
Steps to Solve
- Identify the known values We have a triangle with the following known values:
- Side ( QR = 39.5 )
- Side ( RS = 33.1 )
- Angle ( Q = 55^\circ )
- Use the Law of Cosines to find side ( QS ) The Law of Cosines states that: $$ c^2 = a^2 + b^2 - 2ab \cdot \cos(C) $$
Where:
- ( c ) is the side opposite angle ( C )
- ( a ) and ( b ) are the other two sides
For our triangle, we can set:
- ( a = QR = 39.5 )
- ( b = RS = 33.1 )
- ( C = 55^\circ )
- ( c = QS )
Now we can plug the values into the formula to find ( QS ): $$ QS^2 = 39.5^2 + 33.1^2 - 2 \cdot 39.5 \cdot 33.1 \cdot \cos(55^\circ) $$
- Calculate ( QS^2 ) Now we compute the respective squares and the cosine: $$ QS^2 = 1560.25 + 1095.61 - 2 \cdot 39.5 \cdot 33.1 \cdot 0.5736 $$
Calculating further:
-
Calculate the multiplication: ( 2 \cdot 39.5 \cdot 33.1 \cdot 0.5736 )
-
Deduct from the sum of squares to find ( QS^2 ).
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Calculate side ( QS ) Take the square root of ( QS^2 ): $$ QS = \sqrt{QS^2} $$
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Determine the remaining angles using the Law of Sines Now that we have ( QS ), we can determine the angles ( R ) and ( S ) using the Law of Sines: $$ \frac{a}{\sin(A)} = \frac{b}{\sin(B)} = \frac{c}{\sin(C)} $$
Using:
- ( a = RS = 33.1 )
- ( b = QS )
- ( c = QR = 39.5 )
- ( A = 55^\circ )
Finding angle ( R ): $$ \frac{39.5}{\sin(R)} = \frac{33.1}{\sin(55^\circ)} $$
- Calculate angle ( R ) Rearranging gives: $$ \sin(R) = \frac{39.5 \cdot \sin(55^\circ)}{33.1} $$
Finally, apply the inverse sine: $$ R = \arcsin(\frac{39.5 \cdot \sin(55^\circ)}{33.1}) $$
- Find angle ( S ) For angle ( S ), use: $$ S = 180^\circ - R - 55^\circ $$
The missing parts of the triangle are approximately:
- Side ( QS \approx 30.7 )
- Angle ( R \approx 74.1^\circ )
- Angle ( S \approx 50.9^\circ )
More Information
The Law of Cosines and the Law of Sines are essential tools for solving triangles when given certain sides and angles. Understanding their relationships helps in finding unknown dimensions in geometry.
Tips
- Failing to convert angles properly if using radians instead of degrees.
- Misapplying the Law of Cosines by confusing the sides connected to corresponding angles.
- Not rounding at the correct steps which can lead to a chain of inaccurate results.
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