Find $x$ in equation having Euler's Number I have to find $x$ in this equation. I have already tried cross multiplying but I am not sure what to do after. 
$$
\frac{e^x - e^{-x}}{e^x + e^{-x}} = \frac{3}{4}
$$

We know that $$\sinh x =\frac {e^x -e^{-x}}{2} $$ and that  $$\cosh x =\frac {e^x + e^{-x}}{2} $$ Can you now proceed where $\sinh x $ and $\cosh x $ are hyperbolic trigonometric functions?

We can otherwise put $k =e^x $ and then get our equation as $$\frac {k-\frac {1}{k}}{k+\frac {1}{k}} =\frac {3}{4} $$ $$4 (k^2-1) =3 (k^2+1) $$ $$\Rightarrow k = \sqrt {7} \text { as an acceptable solution} $$ Hope it helps. 
