Finding the critical points of $\sin(x)/x$ and $\cosh(x^2)$ Could someone help me solve this:

What are all critical points of $f(x)=\sin(x)/x$ and $f(x)=\cosh(x^2)$?

Mathematica solutions are also accepted.

As mentioned, there is a solution in each interval $(k \pi, (k+1)\pi)$.  This solution can't be expressed in "closed form", but there is a series in negative powers of $k$:
$$x = (k+1/2)\pi -{\frac {1}{k\pi }}+{\frac {1}{2 \pi \,{k}^{2}}}-{\frac {3\,{
\pi }^{2}+8}{12{\pi }^{3}{k}^{3}}}+{\frac {{\pi }^{2}+8}{8{\pi }^{3}
{k}^{4}}}-{\frac {15\,{\pi }^{4}+240\,{\pi }^{2}+208
}{{240 \pi }^{5}{k}^{5}}}+{\frac {3\,{\pi }^{4}+80\,{\pi 
}^{2}+208}{96{\pi }^{5}{k}^{6}}}+\ldots $$
It looks to me like this  converges for $k \ge 1$ (I'm not sure about $k=1$).
