Originally Posted by
kalagota well, chain rule says that if $\displaystyle h(x)=f(g(x))$, then $\displaystyle h'(x)=f'(g(x))\cdot g'(x)$ of course in the assumption that f and g are differentiable..
so
your $\displaystyle f'(x) = \left[\sec^2{\left(\frac{x}{73}\right)}\right] \cdot \frac{1}{73}$