18) Calcule ∇f(x, y) sendo a)f(x, y) = x2y b)f(x, y) = ex2−y2 c)f(x, y) = x/y d)f(x, y) = arctg(x/y)

a) ∇f(x, y) = (2xy, x^2) b) ∇f(x, y) = (2xe^(x^2-y^2), -2ye^(x^2-y^2)) c) ∇f(x, y) = (1/y, -x/y^2) d) ∇f(x, y) = (1/(1+(x/y)^2), -x/(y(1+(x/y)^2)))