Answer
$tan(tan^{-1}~x) = x$
This graph also looks like the straight line $y=x$
Work Step by Step
Let $~~\theta = tan^{-1}~x$
Then $~~tan~\theta = x$
Therefore, $tan(tan^{-1}~x) = tan~\theta = x$
This graph also looks like the straight line $y=x$