Note that
#color(red)[y=r*sintheta]#
#color(red)[x=r*costheta]#
#y = x^2y-x/y^2 +xy^2#
#(r*sintheta)=(r*costheta)^2*(r*sintheta)-(r*costheta)/(r*sintheta)^2+(r*costheta)(r*sintheta)^2#
#rsintheta=r^3sintheta*cos^2theta-(costheta)/(rsin^2theta)+r^3costheta*sin^2theta#
#[rsintheta-r^3sintheta*cos^2theta-r^3costheta*sin^2theta]/1=-(costheta)/(rsin^2theta)#
#r^2sin^3theta-r^4*sin^3theta*cos^2theta-r^4costheta*sin^4theta=-costheta#
#color(blue)[r^2=(-costheta)/[sin^3theta-r^2*sin^3theta*cos^2theta-r^2costheta*sin^4theta]]#