已知A=8x^2y-6xy^2-3xy,B=7xy^2-2xy+5x^2y,且C=3(A+B),求C-2A的值

问题描述:

已知A=8x^2y-6xy^2-3xy,B=7xy^2-2xy+5x^2y,
且C=3(A+B),求C-2A的值

C-2A=A+3B=(8x^2y-6xy^2-3xy)+(7xy^2-2xy+5x^2y)*3
代入就得解。

C-2A=A+3B
=(8x^2y-6xy^2-3xy)+(7xy^2-2xy+5x^2y)*3
=23x^2y+15xy^2-9xy

∵A=8x²y-6xy²-3xy,B=7xy²-2xy+5x²y ∴C=3(A+B)  =3(8x²y-6xy²-3xy+7xy²-2xy+5x²y)  =3(13x²y+xy²-5xy)  =39x²y+3xy²-15xy ∴C-2A  =39x...