Answer
$e^{4x}$
Work Step by Step
We apply hyperbolic function formulas:
$ \cosh x= \dfrac{e^x+e^{-x}}{2}$ and $ \sinh x= \dfrac{e^x-e^{-x}}{2}$
Thus, $(\sinh x + \cosh x)^4=[\dfrac{e^x-e^{-x}}{2}+\dfrac{e^x+e^{-x}}{2}]^4=[\dfrac{2e^x}{2}]^4=e^{4x}$
