## Archive of posts on Nov 8, 2022

### The point on the circle farthest to two lines

Suppose $P$ is a point on the circle $\odot C$. When is the sum of distances from $P$ to two edges of $\angle O$ extremal? It turns out to be related to angle bisectors (the intersections of $\odot C$ and the bisector of $\angle O$ or its adjacent supplementary angle are extremals), while the edge cases (at the intersections of $\odot C$ and edges of $\angle O$) are a little tricky: we need to use the bisectors to divide the plane into four quadrants, pick the two quadrants where the line intersecting $\odot C$ at $P$ lies, translate the region to make it center at $C$, and see whether $P$ is inside the translated region.

- Categories: math
- Tags: elementary geometry, trigonometry, from zhihu

### Typesetting math in emails

After some comparison among solutions, I use KaTeX to typeset math in my emails.

- Categories: programming
- Tags: jekyll, ruby, tex