A-B-C is a 60-80-40-degree triangle, respectively with I as incenter. Prove that CI = AB. This entry contributed by Sumith Peiris, Moratuwa, Sri Lanka.

Geometry Problems Ten problems: 1381-1390 Visual Index Open Problems All Problems Triangle Incenter Congruence Incenter distance 80-20-80 Isosceles Triangle View or Post a solution