Sangaku problem: two tangents to a circle
Sangaku Problems: Japanese geometrical problems or theorems, in Euclidean geometry
http://en.wikipedia.org/wiki/Sangaku
https://math.osu.edu/sites/math.osu.edu/files/Sangaku.pdf
Two tangents to circle "c" at points B and C meet at point D.
The circle "c" passes through the incenter of the triangle BCD.
Incenter is a point of concurrency formed by intersection of
triangle's angle bisectors.