[1/(a²+2a) -1/(a²+4a+4)]÷[2/(a²+2a)]=[1/a(a+2) -1/(a+2)²]÷[2/a(a+2)]=[1/a(a+2) -1/(a+2)²]×[a(a+2)/2]=(1/2) -a/[2(a+2)]=(1/2) -(a+2-2)/[2(a+2)]=(1/2) -(1/2) +1/(a+2)=1/(a+2)...