Question

Evalaute the following without using a calculator:
cos(13pi/6)

Answer 1

Answer is in the attachment below. Please open it up in a new window to see it in full.

Answer 2

`the\ cos\ function\ is\ periodic:\ \ \ the\ period=2 \pi\\\\cos(2 \pi + \alpha )=cos \alpha \\\\------------------------\\\\cos\bigg{(} \frac{\big{13 \pi }}{\big{6}}\bigg{)}=cos\bigg{(} 2 \pi +\frac{\big{ \pi }}{\big{6}}\bigg{)}=cos\bigg{(} \frac{\big{ \pi }}{\big{6}}\bigg{)}= \frac{\big{ √(3) }}{\big{2}}`