2(x²-xy)-3(2x²-3xy)-2[X²-(2x²-xy+y²

x-y/x²÷x²-2xy+y²/xy*（xy-x²） -3(xy-2x²)-[y²-(5xy-4x²)+2xy] 已知x:y=3:2,求(x²+3xy)/(xy+2xy) 3x²y+xy²-[2xy²-4x²y+（x²y-2xy²） (2x²y-3xy²)-3(x²y-2xy²)+2（x²y-4xy&# 先化简,再求值:{xy(x²-3y)+3xy²}(-2xy)+x³y²(2x-y -3(2x²-xy)+4(x²+xy-6) 化简4xy-3y²-3x²+xy-3xy-2x²+x²-2y² 下列多项式:(1)x²+xy-y²;(2)-x²+2xy-y²;(3)xy+x& 已知x/y=3,求(x²+2xy-3xy²)/(x²-xy+y²) 3x-2xy-8-2x+6xy-x²+6、-x²+2xy-y²-3x²-2xy+ 合并同类项：(2xy²+3xy²)-(6x²y-3xy²)