(1- a²+8/a²+4a+4)除以4a-4/a²+2a
=［a²+4a+4-a²-8]/(a+2)²*a(a+2)/[4(a-1)]
=4(a-1)/(a+2)²*a(a+2)/[4(a-1)]
=a/(a+2).