Chapter 16.7, Problem 2MRE

To determine

To find: $\cos \left(\frac{3\pi }{4}\right)$ =?

Answer to Problem 2MRE

  $-\frac{1}{\sqrt{2}}$

Explanation of Solution

Given: $\cos \left(\frac{3\pi }{4}\right)$

Formula used: $\cos (\pi -\theta )=-\cos \theta$

  $\cos \left(\frac{3\pi }{4}\right)=\cos \left(\pi -\frac{\pi }{4}\right)$

Using the above formula:

  $\cos \left(\pi -\frac{\pi }{4}\right)=-\cos \frac{\pi }{4}=-\frac{1}{\sqrt{2}}$