Is there any quick method of finding if 4 given pts are concyclic or not? (finding the eqn of the circle thru 3 pts and then checking the 4th pt in the eqn is really looooooooooong)
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3 Answers
Lokesh Verma
·2009-03-21 20:12:52
if ABCD are the point
<ACB=<ADC
Chord subtends equal angle
then they are concyclic!
Hari Shankar
·2009-03-22 00:47:17
Ptolemy's theorem - maybe easy since only distances are involved
http://www.cut-the-knot.org/proofs/ptolemy.shtml
Lokesh Verma
·2009-03-22 20:24:12
yes this too..
it was my most favorite theorem in Geometry ptolmey's