Question

先化简,再求值3x^3-(4x^2+5x)-3(x^3-2x^2-2x),其中x=-2

Answer 1

解：原式=（3-3）x^3+(6-4)x^2+(6-5)x
=2x^2+x

带入x=-2
可得原式=2*（-2）^2-2
=2*4-2
=8-2
=6

追问

己知代数式A=6x+4Y-y-5，B=2(x+Y)+(x-3) 当x=Y=-2时求A-B的值

追答

解：A-B
==6x+4Y-y-5-2(x+Y)-(x-3)

=6x+4y-y-5-2x-2y-x+3
=（6-2-1）x+（4-1-2）y-5+3
=3x+y-2
带入x=-2，y=-2，可得原式=3*（-2）-2-2
=-6-2-2
=-10