P = (2, 4)
a = Tangent(P, c)
Q = Point(c)
b = Line(P, Q)
d = OrthogonalLine(P, yAxis)
e = OrthogonalLine(Q, d)
B = Intersect(e, d)
Δy = Segment(B, Q)
Δx = Segment(B, P)