December 4th, 2016, 10:09 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 06:11 AM. 
December 5th, 2016, 07:40 AM  #2 
Global Moderator Joined: Dec 2006 Posts: 20,004 Thanks: 1862 
The answer is 10°, but I don't yet have an elegant proof of this.

December 5th, 2016, 11:32 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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angle, find, measure 
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