# Why is cos -pi/6 the same as cos pi/6?

##### 1 Answer

May 15, 2015

The cosine function is even, which means that

In opposition, the sine function is odd, which means that

You can observe that on the trigonometric circle :

(source : http://en.wikipedia.org/wiki/Unit_circle)

You see that when you have an angle of

In opposition, the ordinate (the