x2y'=x2y2+xy+1．

y'+y²-2ysinx=cosx-sin²x．

y'e^-x+y²-2ye^x=1-e^2x．

[y-x(x²+y²)]dx-xdy=0．

ydx-(1+x+y²)dy=0．

4x²y²dx+2(x³y-1)dy=0．

(x-y²)dx+y(x+1)dy=0．

(x²+y²)dx-2xydy=0．