328. Find the derivative of the function $y=\cos \left(\frac{x}{2}-x^{5}\right)$.
Solution. We have $u=\frac{x}{2}-x^{5}, y=\cos u$. Further, we find $y_{u}^{\prime}=$ $=-\sin u, u_{x}^{\prime}=\frac{1}{2}-5 x^{4}$, from which $y_{x}^{\prime}=-\left(\frac{1}{2}-5 x^{4}\right) \sin \left(\frac{x}{2}-x^{5}\right)$.