where R is the radius of the circumcircle.
If you are not yet familiar with the construction of a circumcircle and the angle properties of a circle, you are advised to look these up first.
The circumcircle
http://www.mathisfunforum.com/viewtopic … 40#p367140
Angle properties of a circle.
http://www.mathisfunforum.com/viewtopic.php?id=17799
Posts 6 and 7
Proof
angle AOF = half angle AOB = ACB (using the angle props)
Therefore
The rest follows by a similar argument.
Bob
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