Answer
$0$
Work Step by Step
We know that $tan$ has a period of $\pi$, hence first we try and find a value where the argument is between $-\frac{\pi}{2}$ and $\frac{\pi}{2}$. Therefore $tan(-3\pi)=tan(-3\pi+2\pi)=tan(-\pi)=tan(-\pi+\pi)=tan(0)=0.$
