March 1st, 2018, 04:59 AM  #1 
Newbie Joined: Feb 2018 From: Kortessem Posts: 1 Thanks: 0  proving a formula
Hello people Can you help me with this?? prove the next formule in a convex quadrilateral ABCD:cos A+cos B+ cos C+ cos D = 4*cos (A+B)/2* cos (B+C)/2* cos (C+A)/2 Thanks! Last edited by greg1313; March 1st, 2018 at 06:08 AM. 

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formula, formule, proving 
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