How do you find the value of cos (pi)/6?
There are 2 ways, that don't need calculator
a. Trig table of special arc -->
b. Use triangle trigonometry
Consider a right triangle ABH that is half of an equilateral triangle
Edit from r3ce:
I believe another option to also look at especially for precalculus if it's applicable is the unit circle. It's basically a picture of certain common values for sine and cosine for angles such as