(1)(x-2xy-y²)dy+y²dx=0
y²dx-2xydy=(y²-x)dy
(y²dx-2xydy)/y^4=(1/y²-x/y^4)dy
d(x/y²)=(1/y²-x/y^4)dy
令x/y²=u
du=(1/y²-u/y²)dy
du/(1-u)=dy/y²
d(1-u)/(1-u)=-dy/y²
ln(1-u)=1/y+C1
1-u=Ce^(1/y)
u=1-Ce^(1/y)
x=y²-Cy²e^(1/y)
(4)(x²+y²+2x)dx+2ydy=0
(x²+y²+2x)dx+d(y²)=0
令y²=u
(x²+2x+u)dx+du=0
u'+u=-x²-2x
u=e^(-x)[∫(-x²-2x)e^xdx+C]=e^(-x)[-x²e^x+C]=-x²+Ce^(-x)
即y²=-x²+Ce^(-x)
另外兩個不會