# Secant Theorem   
Let(A=[-u1,0], B=[u1,0], C=[u2,u3], D=[u4,y1], T=[y2,0]):
Secant := Theorem(
    [not collinear(A,B,C), cocircular(A,B,C,D), intersection(A,B,C,D,T)],
    sdistance(T,A)*sdistance(T,B)-sdistance(T,C)*sdistance(T,D), [y1,y2]);
