(a+5)(a-3)=0,a=-5或a=3
1/a+1-a+2/a^2-1*(a-1)^2/(a+1)(a+2) =1/(a+1)-(a-1)/(a+1)^2=2/(a+1)^2
当a=-5时,原式=1/8
当a=3时,原式=1/8