I am unsure if I have done the following correctly

The question: Differentiate $\displaystyle y=\sqrt{x^2 + \cosh^4x}$

I get my answer as $\displaystyle \frac{dy}{dx} = \frac{1}{2(x^2 + \cosh^4)^2}$

Thanks for any help or suggestions, they are greatly appreciated.

Beard