Solution
= Solution
Differentiating the reciprocal of $1+x^2+y^2$ gives the <gradient>
$$
\boxed{\nabla f(x,y)=\frac{-2}{(1+x^2+y^2)^2}\begin{pmatrix}x\\y\end{pmatrix}.}
$$
= Solution
Differentiating the reciprocal of $1+x^2+y^2$ gives the <gradient>
$$
\boxed{\nabla f(x,y)=\frac{-2}{(1+x^2+y^2)^2}\begin{pmatrix}x\\y\end{pmatrix}.}
$$