Solving for (or approximating) $x$ in $\frac{x-\sin x}{x^{0.4}} = c$ I'm an engineer and I'm deducting a formula, and I found a BIG problem: I can't isolate $x$.
The formula is:
$$\frac{x-\sin x}{x^{0.4}} = c$$
where $c$ is a constant.
How to find the value for $x$, or at least a good approximation?

The leading term of $x-\sin x$ is $\frac{x^3}6$. This would result in a first approximation of $x=(6c)^{1/2.6}$ for smallish values of $c$.
For larger values of $c$ one would use that $|\sin x|\le  1$ to get approximately $x=c^{1/0.6}$.
