a+b=2,a×b=-1求(4a－5b－ab)－﹙2a－7b＋5ab﹚的值

题目

a+b=2,a×b=-1求(4a－5b－ab)－﹙2a－7b＋5ab﹚的值

答案

去括号,得
4a-5b-ab-2a+7b-5ab
=2a+2b-6ab
=2(a+b)-6ab
把a+b=2,ab= -1代人上式,得
4a-5b-ab-2a+7b-5ab
=2a+2b-6ab
=2(a+b)-6ab
=2×2-6×(-1)
=4+6
=10