Theory If z=r(cosθ+isinθ)z=r(\cos\theta+i\sin\theta)z=r(cosθ+isinθ) then Arg(z)=θ\operatorname{Arg}(z)=\thetaArg(z)=θ (up to adding multiples of 2π2\pi2π). Product: Arg(z1z2)=Arg(z1)+Arg(z2) (mod 2π)\operatorname{Arg}(z_1z_2)=\operatorname{Arg}(z_1)+\operatorname{Arg}(z_2)\ (\text{mod }2\pi)Arg(z1z2)=Arg(z1)+Arg(z2) (mod 2π) Quotient: Arg(z1z2)=Arg(z1)−Arg(z2) (mod 2π)\operatorname{Arg}\left(\frac{z_1}{z_2}\right)=\operatorname{Arg}(z_1)-\operatorname{Arg}(z_2)\ (\text{mod }2\pi)Arg(z2z1)=Arg(z1)−Arg(z2) (mod 2π)