I have been taught that the angle between two vectors is supposed to be their inner product. However, the book I'm reading states:

> 
> Recall that the angle between two vectors $u = (u\_0,\ldots,u\_{n−1})$ and $v = (v\_0,\ldots, v\_{n−1})$ in $\mathbb{C}^n$ (the complex plane) is just a scaling factor times their *inner product*.
> 
> 
> 

What is a "scaling factor"?