数学这题不懂啊,完全看不懂啊

解
x^1/2+x^(-1/2)=3
即
√x+1/√x=3
两边平方
x+1/x+2=9
∴x+1/x=7
x^(3/2)+x^(-3/2)
=(x^1/2)³+(x^-1/2)³
=(√x)³+(1/√x)³
=(√x+1/√x)(x-1+1/x)
=3×(7-1)
=3×6
=18
a³+b²=(a+b)(a²-ab+b²)