设圆心C(x,y)
ρ= - √2
θ＝π/4
x=ρcosθ=-1
y=ρsinθ=-1
所以圆C的普通方程为：
(x+1)²+(y+1)²=2
x²+y²+2x+2y=0
ρ²+2ρ(sinθ+cosθ)=0
ρ+2(sinθ+cosθ)=0