Solve / Simplify for x $$\frac{1}{\sqrt{a^{2}-x^{2}}}+\frac{1}{\sqrt{b^{2}-x^{2}}}-\frac{1}{c}=0$$
Hello
I'm wondering whether anyone can help me rearrange this to solve for $x$, where $a$, $b$, $c$ are constants.  I initially thought about a trig substitution $x=b\cdot \cos(z)$ but that just lead to another brick wall. Any insights gratefully appreciated!
Thanks
Guy

Put $1/c$ on one side of the equation, square both sides, separate out the square root and do again so that 
$x$ is a root of $$\begin{multline}x^8+(-2b^2-2a^2+2c^2+2a^2c^2)x^6\\+(-4b^2a^2c^2+a^4-2a^4c^2-4a^2c^2-2b^2c^2+a^4c^4\\+b^4+4b^2a^2-2a^2c^4+c^4)x^4\\+(4b^2a^2c^2+2b^2a^2c^4-2a^4c^4b^2+4a^4c^2b^2+2b^4a^2c^2-2b^4a^2\\-2a^4b^2-2a^2c^4+2a^4c^2+2a^4c^4)x^2\\-2a^4c^4b^2+b^4a^4c^4-2b^4a^4c^2-2a^4c^2b^2+b^4a^4+a^4c^4\end{multline}$$
