[a^(1/2)-a^(-1/2)]^2=a+a^(-1)-2=3-2=1
a^(1/2)-a^(-1/2)=±1
a^(3/2)-a^(-3/2)=[a^(1/2)-a^(-1/2)][a+1+a^(-1)]
=(±1)(3+1)
=±4