I need to solve $a 2^x - x = b$ for $x$ where $a$ and $b$ are parameters. Does it have closed form solution? I need to substitute $x$ in another system of equations in Mathematica.
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Have a look at my answer to your previous question. – Claude Leibovici Jul 04 '18 at 07:35
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$$x = -{\frac {{\rm W} \left(-\ln \left( 2 \right) a{2}^{-b}\right)}{\ln \left( 2 \right) }}-b$$ where $\rm W$ is any branch of the Lambert W function (ProductLog in Mathematica).
But if you have Mathematica, why didn't you ask Mathematica to solve it?
Robert Israel
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I answered https://math.stackexchange.com/questions/2840231/how-to-solve-x-ax-bx-c/2840373#2840373 – Claude Leibovici Jul 04 '18 at 07:36