# Let [.] denote the greatest integer function and $f(x)=[\tan^2x]$ then

$\begin{array}{1 1}(a)\;\lim\limits_{x\to 0}f(x)\;does\;not\;exist\\(b)\;f(x)\;is\;continuous\;at\;x=0\\(c)\;f(x)\;is\;not\;differentiable\;at\;x=0\\(d)\;f'(0)=1\end{array}$

We have $f(x)=[\tan^2x]$
$\tan x$ is an increasing function.