(1+a-3/2)/(a^2-1/4)
=(a-1/2)/[a+1/2)(a-1/2)]
=1/(a+1/2)
=1/(根号2-2+1/2)
=2/(2根号2-3)
=2(2根号2+3)/(8-9)
=-2(2根号2+3)