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Forum URL: http://www.cut-the-knot.org/cgi-bin/dcforum/forumctk.cgi
Forum Name: College math
Topic ID: 612
Message ID: 3
#3, RE: Mahavira's formula for cyclic quadrilaterals
Posted by alexb on May-19-07 at 03:56 PM
In response to message #2
Have a look at

http://www.cut-the-knot.org/proofs/ptolemy.shtml#Mahavira

It's the same as Pierre's remark but perhas a little more detailed. What I want you to do is to make a diagram where you mark the angle theta and think of what cos(theta) signifies, OK?