计算：⑴(3a^2-ab+7)-(-4a^2-2ab+7) (2)3xy-5xy-(-2xy)(3)(-x^2+5+4x)+(5x_数学解答

计算：
⑴(3a^2-ab+7)-(-4a^2-2ab+7) (2)3xy-5xy-(-2xy)
(3)(-x^2+5+4x)+(5x-4+2x^2),其中x=-2

人气：456 ℃　时间：2020-03-31 19:32:16

解答

1 ,(3a^2-ab+7)-(-4a^2-2ab+7)
=3a^2-ab+7+4a^2+2ab-7
=7a^2+ab
2)3xy-5xy-(-2xy)
=3xy-5xy+2xy
=0
3)(-x^2+5+4x)+(5x-4+2x^2)
=-x^2+5+4x+5x-4+2x^2
=x^2+9X+1