# Ptolemy Theorem
Let(A=[-u1,0], B=[u1,0], C=[u2,u3], O=[0,x1], D=[u4,x2]);
Ptolemy := Theorem(
    [arbitrary(A,B,C), circumcenter(A,B,C,O), equidistance(O,D,O,A),
     sdistance(A,B)*sdistance(C,D)-x3^2, sdistance(B,C)*sdistance(A,D)-x4^2,
     sdistance(B,D)*sdistance(A,C)-x5^2], 
    (x3+x4-x5)*(x3+x4+x5)*(x3-(x4-x5))*(x3-(x4+x5)), [x1,x2,x3,x4,x5]);
