Answer
The identity is verified.
$tan(θ+\pi)=tan~θ$
Work Step by Step
$tan(u+v)=\frac{tan~u+tan~v}{1-tan~u~tan~v}$
$tan~\pi=0$
$tan(θ+\pi)=\frac{tan~θ+tan~\pi}{1-tan~θ~tan~θ}=\frac{tan~θ+0}{1-tan~θ(0)}=tan~θ$
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