原式=[(a+2)(a+5)/(a+1)(a+5)][(a²-a+1)/(a+2)²]×[(a+2)/(a²-a+1)]
=[(a+2)/(a+1)][(a²-a+1)/(a+2)²]×[(a+2)/(a²-a+1)]
=(a+2)²(a²-a+1)/[(a+1)(a+2)²(a²-a+1)]
=1/(a+1)
原式=[(a+2)(a+5)/(a+1)(a+5)][(a²-a+1)/(a+2)²]×[(a+2)/(a²-a+1)]
=[(a+2)/(a+1)][(a²-a+1)/(a+2)²]×[(a+2)/(a²-a+1)]
=(a+2)²(a²-a+1)/[(a+1)(a+2)²(a²-a+1)]
=1/(a+1)