\begin{aligned} v \in \mathbb{C}^{1} &= x+iy\\ &=r( \cos \theta+i \sin \theta )\\ &= r\text e^{i\theta} \\ (x,y) &= (r \cos \theta, r \sin \theta) \\ \mathbf v &= (r , \theta) \end{aligned} v C 1 ( x , y ) v = x + i y = r ( cos θ + i sin θ ) = r e i θ = ( r cos θ , r sin θ ) = ( r , θ )
而当 \left\{ \begin{array}{l} e^{i\theta}=\cos \theta+i\sin\theta\\ e^{-i\theta}=\cos\theta-i\sin\theta \end{array} \right. ⇒ \left\{ \begin{array}{l} \cos\theta=\frac{e^{i\theta}+e^{-i\theta}}{2}\\ \sin\theta=\frac{e^{i\theta}-e^{-i\theta}}{2i} \end{array} \right. { e i θ = cos θ + i sin θ e i θ = cos θ i sin θ { cos θ = 2 e i θ + e i θ sin θ = 2 i e i θ e i θ

[1]. https://mengqi92.github.io/2015/10/06/complex/
[2]. https://blog.csdn.net/lanchunhui/article/details/54600285