圆心坐标 ρ=2,θ=3π/4

                 x²+y²=2²,y/x=tan(3π/4)

                 x=-√2, y=√2

圆的直角坐标方程 (x+√2)²+(y-√2)²=3²

圆的极坐标方程   (ρcosθ+√2)²+(ρsinθ-√2)²=3²

   ρ²cos²θ+2+2√2 ρcosθ+ρ²sin²θ-2√2 ρsinθ+2=9

      ρ²+2√2 ρ(cosθ-sinθ)=5

      ρ²+4ρsin(θ+3π/4)=5

或 ρ²+4ρcos(θ+π/4)=5

如图所示