# Tangent Theorem    
Let(A=[x1,0], C=[-x1,0], O=[0,x2], B=[x3,x4], S=[x5,0]):
Tangent := Theorem(
    [arbitrary(A,C,O), equidistance(O,A,O,B), perpendicular(O,B,B,S)],
    sdistance(S,A)*sdistance(S,C)-sdistance(S,B)*sdistance(S,B), [x4,x5]);
