已知A=5x^2y-3xy^2+4xy,B=7xy^2-2xy+x^2y.①求A-2B;②求-1/2(A+B)-A.

已知A=5x^2y-3xy^2+4xy,B=7xy^2-2xy+x^2y.①求A-2B;②求-1/2(A+B)-A.
已知A=5x^2y-3xy^2+4xy,B=7xy^2-2xy+x^2y.①求A-2B;②求-1/2(A+B)-A.

已知A=5x^2y-3xy^2+4xy,B=7xy^2-2xy+x^2y.①求A-2B;②求-1/2(A+B)-A.
.①求A-2B
A-2B
=5x²y-3xy²+4xy-14xy²+4xy-2x²y
=3x²y-17xy²+8xy
;②求-1/2(A+B)-A
-1/2(A+B)-A
=-1/2A-1/2B-A
=-3/2A-1/2B
=-15/2x²y+9/2xy²-6xy-7/2xy²+xy-1/2x²y
=-8x²y+xy²-5xy