In , let be a point on side . Suppose the incircle of touches sides and at respectively, and the incircle of touches sides and at respectively. Suppose the segment intersects and again at and respectively. Show that line , tangent of at and tangent of at are concurrent.
HK-PC 2020
Hong Kong Preliminary Selection Contest and TST 2020.
Other problems
For a sequence with some ones and zeros, we count the number of continuous runs of equal digits in it. (For example the sequence has continuous runs: .) Find the sum of the number of all continuous runs for all possible sequences with ones and zeros.