differentials (calculus)

Question

Let u=f(x)= Find the differential du.

Answer 1

u = f(x) = (x+1)^1/3 / x

du = f'(x)dx = {[x(1/3)(x+1)^-2/3 - (x+1)^1/3] / x²}dx = [(-2x -3) / (3x²(x+1)^2/3)]dx

Answer 2