### Home > A2C > Chapter 11 > Lesson 11.2.1 > Problem11-45

11-45.

$\text{cos}\left(\frac{2\pi}{3}\right) = -\frac{1}{2}$

cos(π) = −1

$\text{cos}\left(-\frac{\pi}{3}\right) = \frac{1}{2}$

Now come up with your own examples.