先化简,再求值：2（x-8)(x+5)-(2x-1)(x+2),其中x=负7

分类: 作业答案 • 2021-12-18 21:47:12

问题描述：

答

2(x-8)(x+5)-(2x-1)(x+2),
=2(x^2-3x-40)-(2x^2+3x-2)
=2x^2-6x-80-2x^2-3x+2
=2x^2-2x^2-6x-3x+2-80
=-9x-78
=-9*(-7)-78
=63-78
=-15

答

2（x-8)(x+5)-(2x-1)(x+2)
=2x²-6x-80-2x²-3x+2
=-9x-78
=63-78
=-15

答

2（x-8)(x+5)-(2x-1)(x+2)
=2(x^2-3x-40)-(2x^2+3x-2)
=2x^2-6x-80-2x^2-3x+2
=-9x-78
=-9×(-7)-78
=63-78
=-15