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[fortpost]

3. 2xydy/dx-y²+x=0
y'-y/(2x)=-1/(2y); z=y² -> y=z^1/2 -> y'=1/2·z^-1/2z'
1/2·z^-1/2z'-1/(2x)·z^1/2=-1/2·z^-1/2
z'-z/x=-1; t=z/x -> z=xt -> z'=t+xt'
t+xt '-t =-1 -> xdt/dx=-1 -> dt=-dx/x -> t=-ln|Cx|
z=xt=-xln|Cx|; y=z^1/2=(-xln|Cx|)^1/2