a+b=2,a×b=-1求(4a－5b－ab)－﹙2a－7b＋5ab﹚的值

a+b=2,a×b=-1求(4a－5b－ab)－﹙2a－7b＋5ab﹚的值
a+b=2,a×b=-1求(4a－5b－ab)－﹙2a－7b＋5ab﹚的值

a+b=2,a×b=-1求(4a－5b－ab)－﹙2a－7b＋5ab﹚的值
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

(4a－5b－ab)－﹙2a－7b＋5ab﹚
=2a+2b-6ab
=2(a+b)-6(ab)
代入
所以原式=4+6=10

10 要步骤的话追问

(4a－5b－ab)－﹙2a－7b＋5ab﹚
=4a-5b-ab-2a+7b-5ab
=2a+2b-6ab
=2(a+b)-6ab
把数带进来
=2×2-6×(-1)
=4+6
=10