The derivative of the function $f(x)$ is $\tan^4 x$. If $f(0) = 0$,then $\lim_{x \to 0} \frac{f(x)}{x}$ is equal to

$\mathop {\lim }\limits_{h \to 0} \frac{{{{(a + h)}^2}\sin (a + h) - {a^2}\sin a}}{h} = $

Find the derivative of the function $(x+a)$ with respect to $x$ (it is to be understood that $a, b, c, d, p, q, r$ and $s$ are fixed non-zero constants and $m$ and $n$ are integers).

Find the derivative of the function $\sin (x+a)$ with respect to $x$ using the first principle,where $a$ is a fixed non-zero constant.

Find the derivative of $x^{2}-2$ at $x=10$.

Find the derivative of the function $f(x) = \frac{1}{x^{2}}$ using the first principle.