已知:A+B=3x^2-5x-1,A-C= - 2x+3x^2-5两式相减A+C=3x²-5x-1+2x-3x²+5=-3x+4已知IxI=1/2 则x=1/2或-1/21.x=1/2时,A+C=-3*(1/2)+4=5/22.x=-1/2时,A+C=-3*(-1/2)+4=11/2(⊙ o ⊙ )应该是B+C吧哦，对，写错了已知:A+B=3x^2-5x-1,A-C= - 2x+3x^2-5两式相减B+C=3x²-5x-1+2x-3x²+5=-3x+4已知IxI=1/2 则x=1/2或-1/21. x=1/2时，B+C=-3*(1/2)+4=5/22. x=-1/2时，B+C=-3*(-1/2)+4=11/2