已知A+B=-3X²-5x-1,A-C=-2x+3x²-5,求B+C的值

问题描述:

已知A+B=-3X²-5x-1,A-C=-2x+3x²-5,求B+C的值

A+B=-3X²-5x-1(1),
A-C=-2x+3x²-5(2)
(1)-(2)得:B+C=-6x²-3x+4

a+b-(a-c)=a+b-a+c=a+c=-3X²-5x-1-(2x+3x²-5)=-6x²-3x+4

∵A+B=-3X²-5x-1,A-C=-2x+3x²-5
∴A+B-﹙A-C﹚=-3X²-5x-1-﹙-2x+3x²-5﹚
∴B+C=-3X²-5x-1+2x-3x²+5
=-6X²-3X+4

A+B-(A-C)
=A+B-A+C
=B+C

B+C=(-3x²-5x-1)-(-2x+3x²-5)=-3x²-5x-1+2x-3x²+5=-3x+4