k = -4.2 (slider from -5 to 5, step 0.1)
f(x) = x^(2.0) + 3.0 * x - 4.0
g(x) = f(x) + k
A = Point(f)
a = Line(A, yAxis)
B = Intersect(g, a, 1.0)
b = Segment(A, B)