My Math Forum About cicumcenter & incenter

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 June 1st, 2018, 09:46 AM #1 Senior Member     Joined: Jan 2012 Posts: 109 Thanks: 2 About cicumcenter & incenter Hi, If, in a triangle ABC, the line joining the circumcenter & the incenter is parallel to BC, show that r = R cos A r = inradius R = circumradius Plz prove it. Thx. Last edited by skipjack; June 2nd, 2018 at 10:50 AM.
 June 1st, 2018, 09:32 PM #2 Global Moderator   Joined: Dec 2006 Posts: 19,285 Thanks: 1681 For any triangle ABC, r = 4R sin(A/2)sin(B/2)sin(C/2) = R(cos A + cos B + cos C - 1). Now click here and scroll down to the end.
 June 1st, 2018, 09:54 PM #3 Senior Member     Joined: Jan 2012 Posts: 109 Thanks: 2 Oh.. I see.. Thx.

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