Solve for x

[Guest]

I need to solve this equation for x. Can anyone help?

[tex]y=\frac{1}{8}x(x-1)+75\frac{2^{(x-1)/7}-1}{1-2^{\frac{-1}{7}}}+ax[/tex]

[Guest]

We cannot solve this unless a value for a is given

[Guest]

I think a-parameter,then y-should not have.

[Guest]

Since this equation has x both as an exponent and as a multiplier, it cannot be solved with elementary functions.
It requires some form of "Lambert's W function": https://en.wikipedia.org/wiki/Lambert_W_function.