Precalculus : Find the Degree Measure of an Angle

Study concepts, example questions & explanations for Precalculus

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Example Questions

Example Question #1 : Angles In The Coordinate Plane

Convert \(\displaystyle \frac{8\pi}{3}\) radians to degrees.

Possible Answers:

\(\displaystyle 360\)

\(\displaystyle 860\)

\(\displaystyle 240\)

\(\displaystyle 900\)

\(\displaystyle 480\)

Correct answer:

\(\displaystyle 480\)

Explanation:

Write the conversion factor between radians and degrees.

\(\displaystyle \pi \textup{ radians} = 180 \textup{ degrees}\)

Cancel the radians unit by using dimensional analysis.

\(\displaystyle (\frac{8\pi}{3} \textup{ radians })(\frac{180 \textup{ degrees}}{\pi \textup{ radians}}) = 480 \textup{ degrees}\)

Example Question #1 : Find The Degree Measure Of An Angle

Convert \(\displaystyle \frac{3}{50}\pi\) to degrees.

Possible Answers:

\(\displaystyle 10.8\)

\(\displaystyle 21.6\)

\(\displaystyle 48\)

\(\displaystyle 3.8\)

\(\displaystyle 16.4\)

Correct answer:

\(\displaystyle 10.8\)

Explanation:

Write the conversion factor of radians and degrees.

\(\displaystyle \pi \textup{ radians}= 180 \textup{ degrees}\)

Substitute the degree measure into \(\displaystyle \pi\).

\(\displaystyle \frac{3}{50}\pi= \frac{3}{50}(180)= 10.8\)

Example Question #295 : Pre Calculus

Determine the angle \(\displaystyle \theta\) in degres made in the plane by connecting a line segment from the origin to \(\displaystyle (-1,-1)\).

 Assume \(\displaystyle \theta >0\)

Possible Answers:

\(\displaystyle \theta= 240^o\)

\(\displaystyle \theta= 245^o\)\(\displaystyle \theta= 45^o\)

\(\displaystyle \theta= 225^o\)

\(\displaystyle \theta= 135^o\)

Correct answer:

\(\displaystyle \theta= 225^o\)

Explanation:

Firstly, since the point \(\displaystyle (-1,-1)\) is in the 3rd quadrant, it'll be between \(\displaystyle 180^o\) and \(\displaystyle 270^o\). If we take \(\displaystyle 180^o\) to be the horizontal, we can form a triangle with base and leg of values \(\displaystyle -1\) and \(\displaystyle -1\). Solving for the angle in the 3rd quadrant given by \(\displaystyle \gamma\)

\(\displaystyle tan(\gamma)=\frac{-1}{-1}=1\)

\(\displaystyle \gamma=45^o\)

Since this angle is made by assuming \(\displaystyle 180^o\) to be the horizontal, the total angle measure \(\displaystyle \theta\) is going to be:

 \(\displaystyle \theta=180^o+45^o=225^o\)

Example Question #296 : Pre Calculus

Find the degree measure of \(\displaystyle \frac{11}{8} \pi\) radians.  Round to the nearest integer.

Possible Answers:

\(\displaystyle 248\)

\(\displaystyle 237\)

\(\displaystyle 242\)

\(\displaystyle 215\)

\(\displaystyle 258\)

Correct answer:

\(\displaystyle 248\)

Explanation:

In order to solve for the degree measure from radians, replace the \(\displaystyle \pi\) radians with 180 degrees.  

\(\displaystyle \pi \textup{ radians} = 180 \textup{ degrees}\)

\(\displaystyle \frac{11}{8} (180) = \frac{11\times 45}{2} = \frac{495}{2}= 247.5\)

The nearest degree is \(\displaystyle 248\).

Example Question #297 : Pre Calculus

Given a triangle, the first angle is three times the value of the second angle.  The third angle is \(\displaystyle \frac{\pi}{3} \textup{ radians}\).  What is the value of the second largest angle in degrees?

Possible Answers:

\(\displaystyle 120\)

\(\displaystyle 30\)

\(\displaystyle 45\)

\(\displaystyle 90\)

\(\displaystyle 60\)

Correct answer:

\(\displaystyle 60\)

Explanation:

A triangle has three angles that will add up to \(\displaystyle 180\) degrees.

Convert the radians angle to degrees by substituting \(\displaystyle 180 \textup{ degrees}\) for every \(\displaystyle \pi \textup{ radian}\).

\(\displaystyle \frac{180}{3} = 60 \textup{ degrees}\)

The third angle is 60 degrees.

Let the second angle be \(\displaystyle x\).  The first angle three times the value of the second angle is \(\displaystyle 3x\).  Set up an equation that sums the three angles to \(\displaystyle 180 \textup{ degrees}\).

\(\displaystyle 3x+x+60 = 180\)

Solve for \(\displaystyle x\).

\(\displaystyle 4x+60 = 180\)

\(\displaystyle 4x=120\)

\(\displaystyle x=30\)

Substitute \(\displaystyle x=30\) for the first angle and second angle.

The second angle is:  \(\displaystyle x=30\)

The first angle is:  \(\displaystyle 3x= 3(30) = 90\)

The three angles are:  \(\displaystyle 30,60,90\)

The second highest angle is:  \(\displaystyle 60\)

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