(2а-3b)(5a+b)-10(a+b)^2= (2a-3b)(5a+b)-10(a+b)(a+b) = (10a2+2ab-15ab-3b2)-10(a+b)(a+b) = 1(10a2+2ab-15ab-3b2)+(-10a2-10ab-10ab-10b2) = 10a2+2ab-15ab-3b2+(-10a2-10ab-10ab-10b2) = 10a2+2ab-15ab-3b2-10a2-10ab-10ab-10b2 = – 33ab – 13b2
(2а-3b)(5a+b)-10(a+b)^2= (2a-3b)(5a+b)-10(a+b)(a+b) = (10a2+2ab-15ab-3b2)-10(a+b)(a+b) = 1(10a2+2ab-15ab-3b2)+(-10a2-10ab-10ab-10b2) = 10a2+2ab-15ab-3b2+(-10a2-10ab-10ab-10b2) = 10a2+2ab-15ab-3b2-10a2-10ab-10ab-10b2 = – 33ab – 13b2