用指数形式来表示
z1=r1e^(iθ1),z2=r2e^(iθ2)
│z1*z2│= |r1*r2*e^[i(θ1+θ2)]| = |r1*r2|
│z1|*|z2│ = |r1e^(iθ1)| * |r2e^(iθ2)|=|r1|*|r2|
于是两式相等