a = 1.5 (slider from -5 to 5)
f(x) = (a * x)
B = Point(f)
h = OrthogonalLine(B, yAxis)
C = Intersect(h, yAxis)
i = Segment(B, C)
g = OrthogonalLine(B, xAxis)
A = Intersect(g, xAxis)
j = Segment(B, A)
texte1: "f(x)=" + (LaTeX[a]) + "x"