计算定积分（1 4） √x(1-√x)dx

∫(1→4) √x•(1 - √x) dx
= ∫(1→4) (√x - x) dx
= (2/3)x^(3/2) - x²/2|(1→4)
= [(2/3)(8) - 8] - [2/3 - 1/2]
= -17/6