Question

1,已知A=2x^2+3xy-2x-1,B=-x^2+xy-1,且3A＋6B的值与x无关,求y的值

Answer 1

1.3A+6B= 3(2x^2+3xy-2x-1)+6(-x^2+xy-1)=15xy-6x-9

若与x无关

则15xy-6x=0所以5y-2=0

y=2/5

2.(1)A-2B=5x^2y-3xy^2+4xy-2（7xy^2-2xy+x^2y）=-17xy^2+3x^2y+8xy

(2)A+B+2C=5x^2y-3xy^2+4xy+2（7xy^2-2xy+x^2y）=11xy^2+7x^2y+2C=0

所以C=-(11xy^2+7x^2y)/2

C-A=-(11xy^2+7x^2y)/2-(5x^2y-3xy^2+4xy)=-5xy^2/2-17x^y/2-4xy

希望你能满意,谢谢