Answer
Undefined.
Work Step by Step
$\tan [(2n+1)\cdot 90^{\circ}]=\frac{\sin[(2n+1)\cdot90^{\circ}]}{\cos [(2n+1)\cdot90^{\circ}]}$
But denominator=$\cos[(2n+1)\cdot 90^{\circ}]=0$
As denominator vanishes, $\tan[(2n+1)\cdot 90^{\circ}]$ is undefined.
