原式=[(a²-2ab)/(-ab+b²)]÷{[a/(a+b)]÷[2ab/(2b-a)]}
={[a(a-2b)]/[-b(a-b)]}÷{[a/(a+b)]×[-(a-2b)/(2ab)]}
={[a(a-2b)/[-b(a-b)]}÷{-(a-2b)/[2b(a+b)]}
={[a(a-2b)/[-b(a-b)]}×[-2b(a+b)/(a-2b)]
=2a(a+b)/(a-b)
原式=[(a²-2ab)/(-ab+b²)]÷{[a/(a+b)]÷[2ab/(2b-a)]}
={[a(a-2b)]/[-b(a-b)]}÷{[a/(a+b)]×[-(a-2b)/(2ab)]}
={[a(a-2b)/[-b(a-b)]}÷{-(a-2b)/[2b(a+b)]}
={[a(a-2b)/[-b(a-b)]}×[-2b(a+b)/(a-2b)]
=2a(a+b)/(a-b)