# Even and Odd Trigonometric Functions

Points P_t and P_(-t) of unit circle has same x-coordinate and same y-coordinates with opposite signs (see figure).

This means that cos(-t)=cos(t), sin(-t)=-sin(t), i.e. function y=cos(x) is even and function y=sin(x) is odd. From definition it follows that functions y=tan(x) and y=cot(x) are odd.