已知A等于2x²y-3y² ,B=－5xy²+y² 且A+B+C=0求C

已知A等于2x²y-3y² ,B=－5xy²+y² 且A+B+C=0求C
已知A等于2x²y-3y² ,B=－5xy²+y² 且A+B+C=0求C

已知A等于2x²y-3y² ,B=－5xy²+y² 且A+B+C=0求C
A+B+C=0.
则C=-A-B=-(2x²y-3y² )-(-5xy²+y² )
=-2x²y+3y²+5xy²-y²
=-2x²y+2y²+5xy².

C=-(A+B)=-2x²y+5xy²+2y²

C=-A-B=-2x²y+3y²+5xy²-y²=5xy²-2x²y+2y²