Trigonometry : Complementary and Supplementary Angles

Study concepts, example questions & explanations for Trigonometry

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Example Questions

Example Question #31 : Complementary And Supplementary Angles

Find the supplementary angle of \(\displaystyle \frac{\pi}{4}\) :

Possible Answers:

\(\displaystyle \frac{\pi}{4}\)

\(\displaystyle \frac{3\pi}{4}\)

\(\displaystyle \frac{\pi}{2}\)

\(\displaystyle -\frac{\pi}{4}\)

\(\displaystyle \frac{7\pi}{4}\)

Correct answer:

\(\displaystyle \frac{3\pi}{4}\)

Explanation:

Since the given angle is in radians to find the supplementary angle we need to subtract the giving angle from \(\displaystyle \pi\).

Hence, 

\(\displaystyle \pi-\frac{\pi}{4}=\frac{3\pi}{4}\)

Example Question #32 : Complementary And Supplementary Angles

Find the supplementary angle of \(\displaystyle \frac{5\pi}{8}\) 

Possible Answers:

\(\displaystyle -\frac{5\pi}{8}\)

\(\displaystyle \frac{11\pi}{8}\)

\(\displaystyle \frac{\pi}{8}\)

The supplementary angle of \(\displaystyle \frac{5\pi}{8}\) does not exist, because \(\displaystyle \frac{5\pi}{8}\) is larger than \(\displaystyle \frac{\pi}{2}\).

\(\displaystyle \frac{3\pi}{8}\)

Correct answer:

\(\displaystyle \frac{3\pi}{8}\)

Explanation:

Since the given angle is in radians to find the supplementary angle we need to subtract the giving angle from \(\displaystyle \pi\).

Hence,

\(\displaystyle \pi-\frac{5\pi}{8}=\frac{3\pi}{8}\)

Example Question #32 : Complementary And Supplementary Angles

What is the supplementary angle to \(\displaystyle 110\degree\)?

Possible Answers:

\(\displaystyle 60\degree\)

\(\displaystyle 75\degree\)

\(\displaystyle 40\degree\)

\(\displaystyle 70\degree\)

Correct answer:

\(\displaystyle 70\degree\)

Explanation:

Supplementary angles, by definition, add up to \(\displaystyle 180\degree\).

To find the other angle, you set up the equation 

\(\displaystyle 110\degree+x=180\degree\).

Solving the equation gets 

\(\displaystyle x=70\degree\).

Example Question #33 : Complementary And Supplementary Angles

List the complement and the supplement for \(\displaystyle \small \frac{\pi}{4}\).

Possible Answers:

\(\displaystyle \frac{\pi}{4}\) and \(\displaystyle \frac{-3\pi}{4}\)

\(\displaystyle \small \frac{\pi}{4}\) and \(\displaystyle \small \frac{3\pi}{4}\)

\(\displaystyle \small \frac{\pi}{4}\) and \(\displaystyle \small \frac {7\pi}{4}\)

\(\displaystyle \small \frac{3\pi}{4}\) and \(\displaystyle \frac{7\pi}{4}\)

\(\displaystyle \small \small \frac{5\pi}{4}\) and \(\displaystyle \small \frac{-3\pi}{4}\)

Correct answer:

\(\displaystyle \small \frac{\pi}{4}\) and \(\displaystyle \small \frac{3\pi}{4}\)

Explanation:

To find the complement of \(\displaystyle \frac{\pi}{4}\), subtract it from \(\displaystyle \frac{\pi}{2}\), or equivalently, \(\displaystyle \frac{2\pi}{4}\):

\(\displaystyle \frac{2\pi}{4} - \frac{\pi}{4} = \frac{1\pi}{4}\)

To find the supplement of \(\displaystyle \frac{\pi}{4}\), subtract it from \(\displaystyle \pi\), or equivalently \(\displaystyle \frac{4\pi}{4}\):

\(\displaystyle \small \frac{4\pi}{4} - \frac{\pi}{4} = \frac{3\pi}{4}\)

Example Question #33 : Angles

Which angle is \(\displaystyle \frac{2}{3}\) its supplement?

Possible Answers:

\(\displaystyle \small \frac{2\pi}{5}\)

\(\displaystyle \small \frac{6\pi}{5}\)

\(\displaystyle \small \frac{5\pi}{3}\)

\(\displaystyle \frac{5\pi}{6}\)

\(\displaystyle \small \frac{3\pi}{10}\)

Correct answer:

\(\displaystyle \small \frac{2\pi}{5}\)

Explanation:

There are many ways to solve this problem. Regardless, we need to know that supplementary angles add together to \(\displaystyle \pi\). To figure out what plus \(\displaystyle \frac{2}{3}\) of itself would equal \(\displaystyle \pi\), we can set up this equation:

\(\displaystyle \small x + \frac{2}{3}x = \pi\) to combine like terms, create common denominators

\(\displaystyle \small \frac{3}{3}x + \frac{2}{3}x = \pi\)

\(\displaystyle \small \frac{5}{3}x = \pi\) multiply both sides by the reciprocal, \(\displaystyle \small \frac{3}{5}\)

\(\displaystyle \small x = \pi * \frac{3}{5 }\)

\(\displaystyle \small x = \frac{3\pi}{5}\)

Our actual answer is going to be \(\displaystyle \small \frac{2}{3}\) of this, since the angle that we are looking for is \(\displaystyle \frac{2}{3 }\) of its supplement. In other words, we just found x, and the angle that we are looking for is \(\displaystyle \small \frac{2}{3}x\):

\(\displaystyle \small \frac{2}{{\color{DarkOrange} 3}}*\frac{{\color{DarkOrange} 3}\pi}{5} = \frac{2}{1} * \frac{\pi}{5 }= \frac{2\pi}{5}\)

Our answer is \(\displaystyle \small \frac{2\pi}{5}\).

 

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