√x +1/√x =3 则 (√x +1/√x)³ = x^(3/2) + x^(-3/2) + 3 (√x +1/√x) x^(3/2) + x^(-3/2) = 3³ - 3*3 = 18 x^(3/2) + x^(-3/2) -2 = 18-2 =16
