Archive of posts with tag “elementary geometry”

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.
/math #elementary geometry #trigonometry #from zhihu