### Home > PC3 > Chapter 2 > Lesson 2.3.3 > Problem2-155

2-155.

State the exact value of each of the following trigonometric expressions without using a calculator or referring to your unit circle.

1. $\cos\left(\frac{-5\pi}{6}\right)$

$-\frac{5\pi}{6}=-\frac{5\pi}{6}+2\pi=\frac{7\pi}{6}$

What is $\cos\Big(\frac{7\pi}{6}\Big)$?

1. $\tan\left(\frac{31\pi}{4}\right)$

$\frac{31\pi}{4}=\frac{31\pi}{4}-6\pi=\frac{7\pi}{4}$