just use the transformation equivalent
x=r cos thetax=rcosθ and y=r sin thetay=rsinθ in the equation
xy=x-2y+y^2xy=x−2y+y2
so that xy=x-2y+y^2xy=x−2y+y2 becomes
r cos theta* r sin theta=r cos theta-2* r sin theta+ (r sin theta)^2rcosθ⋅rsinθ=rcosθ−2⋅rsinθ+(rsinθ)2
canceling some of the r
r* cos theta* sin theta= cos theta-2* sin theta+ r sin^2 thetar⋅cosθ⋅sinθ=cosθ−2⋅sinθ+rsin2θ
simplify to obtain
r* (cos theta* sin theta- sin^2 theta)= cos theta-2* sin thetar⋅(cosθ⋅sinθ−sin2θ)=cosθ−2⋅sinθ
and
r=(cos theta-2* sin theta)/(cos theta* sin theta- sin^2 theta)r=cosθ−2⋅sinθcosθ⋅sinθ−sin2θ
have a nice day!