b = 4 (slider from -5 to 5, step 0.1)
c = -3 (slider from -5 to 5, step 0.1)
a = 0.2 (slider from -5 to 5, step 0.1)
b_1: x = b
c_1: x = c
f(x) = a * (x - b) * (x - c)