Question

Answer the following. (a) Find an angle between 0 and 2π that is coterminal with -13T/12 (b) Find an angle between 0° and 360° that is coterminal with 810°. Give exact values for your answers.

Answer 1

(a) Find an angle between 0 and 2π that is coterminal with -13π/12.

To get coterminal angles, we simply have to add or subtract 2π. In this problem, we are looking for a coterminal angle that is between 0 and 2π, so we will add 2π to -13π/12:

$\frac{-13\pi}{12}+2\pi=\frac{11\pi}{12}$

(b) Find an angle between 0° and 360° that is coterminal with 810°.

Similarly to the previous exercise, we will substract 360° to 810° to find a coterminal angle that is between 0 and 360°:

$\begin{gathered} 810\text{\degree}-360\text{\degree}=450\text{\degree} \\ 450\text{\degree}-360\text{\degree = 90\degree} \end{gathered}$

ANSWER

a. 11π/12

b. 90°