x=rhocosthetax=ρcosθ from which costheta=x/rhocosθ=xρ y=rhosinthetay=ρsinθ from which sintheta=y/rhosinθ=yρ rho=root2(x^2+y^2)ρ=2√x2+y2 rho^2=x^2+y^2ρ2=x2+y2 rho^2=18sinthetacostheta=ρ2=18sinθcosθ= rho^2=18(xy)/rho^2ρ2=18xyρ2 rho^4=18xyρ4=18xy (x^2+y^2)^2=18xy(x2+y2)2=18xy