(d)
Given, $f(x) = \frac{g(x) + g( - x)}{2} + \frac{2}{\left\lbrack h(x) + h( - x) \right\rbrack^{- 1}}$
$\Rightarrow (x) = \frac{g(x) + g( - x)}{2} + 2\left\lbrack h(x) + h( - x) \right\rbrack$
On differentiating w.r.t. $x,\$we get
$f^{'}(x) = \frac{g^{'}(x) - g^{'}( - x)}{2} + 2\lbrack h^{'}(x) - h^{'}( - x)\rbrack$
$\therefore{\ f}^{'}(0) = \frac{g^{'}(0) - g^{'}(0)}{2} + 2\lbrack h^{'}(0) - h^{'}(0)\rbrack$
= 0