由x=ρcosθ,y=ρsinθ ,得 cosθ=x/ ρ sinθ=y/ ρ且x^2+y^2=ρ^2而ρ=cos(π/4-θ)=cosπ/4cosθ+sinπ/4sinθ=√2/2(cosθ+sinθ)故ρ=√2/2(cosθ+sinθ)=√2/2(x/ ρ+y/ ρ）此式两端同乘以以ρ得,ρ^2=√2/2(...