已知A=x3-2x2+4x+3,B=x2+2x-6,C=x3+2x-3,求:A-(B+C)的值,其中x=-2.

问题描述:

已知A=x3-2x2+4x+3,B=x2+2x-6,C=x3+2x-3,求:A-(B+C)的值,其中x=-2.

A-(B+C)=(x3-2x2+4x+3)-[(x2+2x-6)+(x3+2x-3)]
=(x3-2x2+4x+3)-[x2+2x-6+x3+2x-3]
=x3-2x2+4x+3-x2-2x+6-x3-2x+3
=x3-x3-2x2-x2+4x-2x-2x+3+3+6
=-3x2+12,
当x=-2时,原式=-3×(-2)2+12=-12+12=0.