T(P,QR) denotes the tangential distance |PS|,

where point P lies outside C(QR), point S

lies on C(QR), and PS is tangent to C(QR).

Let A, B, C, and D be distinct, collinear

points in that order.

Construct a point E on line AD such that

|EF| = T(E,AB) = T(E,CD) = |EG|