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June 1st, 2018, 09:46 AM   #1
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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.
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June 1st, 2018, 09:32 PM   #2
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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.
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June 1st, 2018, 09:54 PM   #3
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Oh.. I see.. Thx.
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