联立解 y = x 与 x = y^2 得交点 O(0, 0), P(1, 1)

S = ∫<0, 1> (√x-x)dx = [(2/3)x^(3/2) - X^2/2]<0, 1> = 1/6

Vx = π∫<0, 1> (x-x^2)dx = π[x^2/2-x^3/3]<0, 1> = π/6