A = (5, 1)
m: y(A) / x(A)
P = (1, 5)
O = Intersect(xAxis, yAxis)
d = Vector(O, A)
r = Line(P, d)
B = Intersect(r, yAxis)
f(x) = m x + y(B)
T4: "y = " + f
G = (7, 4)
b = OrthogonalLine(G, r)
c = Line(G, r)