1+(2x-4)/(x^2-a-2)]/[(x+3)/(x^2-1)]
={1+2(x-2)/[(x-2)(x+1)]}(x^2-1)/(x+3)
=[1+2/(x+1)](x+1)(x-1)/(x+3)
=[x+1+2](x-1)/(x+3)
=x-1
x=√3 （根3）
原式=√3-1.