Let $f(x + y) = f(x) + f(y)$ and $f(x) = x^2 g(x)$ for all $x, y \in R$,where $g(x)$ is a continuous function. Then $f'(x)$ is equal to

$\mathop {\text{Limit}}\limits_{h \to 0} \frac{{\int\limits_a^{x + h} {\ln^2 t \, dt} - \int\limits_a^x {\ln^2 t \, dt} }}{h} = $

If $y=\frac{x \sin ^{-1} x}{\sqrt{1-x^2}}+\log \sqrt{1-x^2}$, then $\frac{d y}{d x}=$

If $y=\sqrt{\frac{1+\tan x}{1-\tan x}}$,then $\frac{d y}{d x}=$

If $f(x) = \frac{\sin^2 x}{1+\cot x} + \frac{\cos^2 x}{1+\tan x}$,then the value of $f^{\prime}\left(\frac{\pi}{6}\right)$ is equal to

If $y(\alpha)=\sqrt{2\left(\frac{\tan \alpha+\cot \alpha}{1+\tan ^{2} \alpha}\right)+\frac{1}{\sin ^{2} \alpha}}$ for $\alpha \in\left(\frac{3 \pi}{4}, \pi\right)$,then find $\frac{d y}{d \alpha}$ at $\alpha=\frac{5 \pi}{6}$.