([SIZE="2"]Moderator's note: thread moved from "Differential Equations")
M(x,y) + N(x,y)(dy/dx) = 0
f'(xy) = G(xy)f(xy) where G(xy) = (Nx - My)/(xM - yN)
Replace xy with a single variable to obtain a simple 1st order differential equation and find f(xy).
I got to:
ln|f| =...