a = 1.9 (slider from -5 to 5, step 0.1)
x_1 = 2 (slider from -5 to 5, step 0.5)
x_2 = 1 (slider from -5 to 5, step 0.5)
x_3 = 4 (slider from -5 to 5, step 0.5)
f(x) = (((a * (x - x_1)) * (x - x_2)) * (x - x_3))
texte1: "x_1=" + x_1 + "
x_2=" + x_2 + "
x_3=" + x_3 + "
f(x)=" + f + ""