(xy－y+)－(xy－x+)；

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f(x，y)=3(x+y)+32xy f(x，y)=3(x+y)-32xy f(x，y)=3(x+y)-16xy f(x，y)=3(x+y)+16xy

2x²y³+y+3xy 2x²y²﹣2y+3xy 2x²y³+2y﹣3xy 2x²y³+y﹣3xy

f(x,y)=3(x+y)-32xy f(x,y)=3(x+y)-16xy f(x,y)=3(x+y)+32xy f(x,y)=3(x+y)+16xy

f（x，y）=3（x+y）+32xy f（x，y）=3（x+y）-32xy f（x，y）=3（x+y）-16xy f（x，y）=3（x+y）+16xy

3x²y-4xy²； x²y-4xy²； x²y+2xy²； -x²y-2xy²

xy(2x－2y)² 2xy(x－y)² 4xy(x²－2xy+y²) 4xy(x－y)²

e^xy[xsin(x+y)-cos(x+y)] e^xy[xsin(x+y)+cos(x+y)] e^xy[xsinxy+cos(x+y)] e^xy[ysin(x+y)+xcos(x+y)]

f(x，y)=3(x+y)+32xy f(x，y)=3(x+y)-32xy f(x，y)=3(x+y)-16xy f(x，y)=3(x+y)+16xy

xy＜0 xy＞0 x＞0，y＞0 x＜0，y＜0

44+XY和X.、Y 44+XY和22+Y 22+XY和X.、Y 44+XY和22+X、22+Y

e^xy[xsin(x+y)-cos(x+y)] e^xy[xsin(x+y)+cos(x+y)] e^xy[xsinxy+cos(x+y)] e^xy[ysin(x+y)+xcos(x+y)]

只有Ⅱ 只有Ⅲ Ⅰ和Ⅲ Ⅱ和Ⅳ

f(x，y)=3(x+y)+32xy f(x，y)=3(x+y)-32xy f(x，y)=3(x+y)-16xy f(x，y)=3(x+y)+16xy

e^xy[xsin(x+y)-cos(x+y)] e^xy[xsin(x+y)+cos(x+y)] e^xy[xsinxy+cos(x+y)] e^xy[ysin(x+y)+xcos(x+y)]

8x²y-24xy²=8xy（x-3y）; ax+bx+ay+by=x（a+b）+y（a+b） 12x²y+14x²y²-2xy=2xy（6x+7xy-1）; x³-8=（x-2）（x²+2x+4）

2x²-xy-x=2x(x-y-1) -xy²+2xy-3y=-y(xy-2x-3) x(x-y)-y(x-y)=(x-y)² x²-x-3=x(x-1)-3