Chapter 9.3, Problem 21E

Solution

To sketch: the given angle and to find its reference angle.

  

The reference angle is ${\theta }^{\prime }=\frac{\pi }{3}$ .

Given:

  $\frac{8\pi }{3}$ .

Calculation:

Let $\theta =\frac{8\pi }{3}$ .

Now the sketch of the given angle is,

  

Here, the terminal side of $\theta$ lies in Quadrant II.

So, the reference angle is

  $\begin{array}{c}{\theta }^{\prime }=3\pi -\frac{8\pi }{3}\\ =\frac{\pi }{3}\end{array}$