a

a = 1 (slider from -5 to 5, step 0.1)
b = -2 (slider from -5 to 5, step 0.1)
c = -1 (slider from -5 to 5, step 0.1)
f(x) = a * x^(2.0) + b * x + c
f'(x) = f'(x)
A = Intersect(f', xAxis)
a_2 = OrthogonalLine(A, xAxis)
S = Intersect(f, a_2)