Question

(a-2b)的平方+(a-b)(a+b)-2(a-3b)(a-b),当a=2分之1,b=-3时的值是多少?

Answer 1

(a-2b)²+(a-b)(a+b)-2(a-3b)(a-b)

=(a²-4b+4b²)+(a²-b²)-2(a²-4ab+3b²)

=a²-4b+4b²+a²-b²-2a²+8ab-6b²

=-4b-3b²+8ab

=-4(-3)-3(-3)²+8(1/2)(-3)

=12-27-12

=-27