 Solution

ID: past-exam-of-the-options-ii-course-of-the-university-of-oxford/2011/f/f2/b/i/solution

Differentiating the reciprocal of

1 + x^{2} + y^{2}

gives the gradient

\nabla f (x, y) = \frac{- 2}{( 1 + x ^{2} + y ^{2} ) ^{2}} (x y) .

 New to topics? Read the docs here!