TITLE: Given two vectors, how can I denote the angle between them?
QUESTION [13 upvotes]: Given the vectors $\vec{a}$ and $\vec{b}$, how can I denote the angle between them?

REPLY [3 votes]: You can explicitly denote it once, i.e. give it a variable name like $\theta_{ab}$. For example,

..., where $\theta_{ab}$ denotes the angle between vector $\vec{a}$ and $\vec{b}$.

From there on, you just write $\theta_{ab}$, and all should be clear.