#### Answer

$$\nabla f =\left\langle-2x\sin \left(x^{2}+y\right),-\sin \left(x^{2}+y\right) \right\rangle$$

#### Work Step by Step

Given
$$ f(x, y)=\cos \left(x^{2}+y\right) $$
Then
\begin{align*}
\nabla f&=\left\langle\frac{\partial f}{\partial x}, \frac{\partial f}{\partial y} \right\rangle\\
&=\left\langle-2x\sin \left(x^{2}+y\right),-\sin \left(x^{2}+y\right) \right\rangle
\end{align*}