Ptolemy's Theorem

# AB.CD+BC.DA=AC.BD

Ptolemy:=proc() local A,B,C,D,i,t1,t2,t3,t4,R:

A:=ParamCircle([0,0],R,t1): B:=ParamCircle([0,0],R,t2):
C:=ParamCircle([0,0],R,t3): D:=ParamCircle([0,0],R,t4):

SumSqRtsIsZero([
DeSq(A,B)*DeSq(C,D),
DeSq(B,C)*DeSq(D,A),
DeSq(A,C)*DeSq(B,D)]):

end:

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