My Math Forum Find the measure of the angle

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 December 4th, 2016, 09:09 AM #1 Newbie   Joined: Dec 2016 From: Romania Posts: 2 Thanks: 0 I have a geometry problem to solve: in the triangle ABC, the measure of BAC=120, ABC=20. In the inside of the triangle is a point O so that the measure of OAB=100 and OBA=10. Find the measure of OCA. Thank you for the help. Last edited by skipjack; December 5th, 2016 at 05:11 AM.
 December 5th, 2016, 06:40 AM #2 Global Moderator   Joined: Dec 2006 Posts: 20,373 Thanks: 2010 The answer is 10°, but I don't yet have an elegant proof of this.
 December 5th, 2016, 10:32 AM #3 Newbie   Joined: Dec 2016 From: Romania Posts: 2 Thanks: 0 that's true, we have to proof this without using trigonometry

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