(2a+b)(b-2a)-b(5b-8a)
=-4a²+b²-5b²+8ab
=-4(a²-2ab+b²)
=-4(a-b)²
-4(a-b)²
(2a+b)(b-2a)-b(5b-8a)
=b²-4a²-5b²+8ab
=-(4a²-8ab+4b²)
=-4(a²-2ab+b²)
=-4(a-b)²
(2a+b)(b-2a)-b(5b-8a)
b²-4a² - 5b² + 8ab
= - ( 4a²-8ab+ 4b²)
= - 2(a-b)²
原式=b²-4a²-5b²+8ab
=-4(a²-2ab+b²)
=-4(a-b)²