x^1/2+x^-1/2=3
两边平方
x+2+x^-1=9
x+x^-1=7
两边平方
x^2+2+x^-2=49
x^2+x^-2=47
x^3/2+x^-3/2
=(x^1/2+x^-1/2)(x-1+x^-1)
=3*(7-1)
=18
所以原式=(18-3)/(47-2)
=1/3