# 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.