Discontinuity at the origin

Study the continuity on $R^{2}$ of the function

f (x, y) = ⎩ ⎨ ⎧ \frac{( x + y ) ^{2}}{x ^{2} + y ^{2}} 1 (x, y) \neq = (0, 0) (x, y) = (0, 0)

The full solution of this exercise is in the unlocked version.