(1)5(a+b)ˆ²+(a+b)-(a+b)ˆ2-4(a+b)
=4(a+b)ˆ²-3(a+b)
(2)3(x-y)ˆ2-7(x-y)+8(x-y)ˆ2+6(x-y)
=11(x-y)ˆ2-(x-y)