如上所示
是抛物线
cosθ = x/ρ, sinθ = y/ρρ = (2 + 2x/ρ)/(y/ρ)² = 2ρ(ρ + x)/y²y² = 2(ρ + x) = 2[√(x²+y²) + x]y²/2 - x = √(x²+y²) 平反再简化，可得y² = 4(1+x)
