314. Find the derivative of the function $y=\sin \left(x^{3}-3 x^{2}\right)$.
Solution. Here $u=x^{3}-3 x^{2}, y=\sin u$. We find $u_{x}^{\prime}=\left(x^{3}-\right.$ $\left.-3 x^{2}\right)^{\prime}=3 x^{2}-6 x$. Then $y_{x}^{\prime}=y_{u}^{\prime} u_{x}^{\prime}=\left(3 x^{2}-6 x\right) \cos \left(x^{3}-3 x^{2}\right)$.