$ \mathscr{C}_f $

a = -2 (slider from -2 to 2, step 0.1)
b = -1 (slider from -5 to 5, step 0.5)
c = 1.5 (slider from -5 to 5, step 0.5)
f(x) = a * x^(2) + b * x + c
k: (-b) / (2 * a)
l: f(k)
A = Point(f)
texte2: "$ f(x) = a x^2 + b x + c =" + (LaTeX[f]) + ""
texte1: "$ \mathcal{S}  = \left(\frac{-b}{2a} ; f\left( \frac{-b}{2a}  \right)   \right) = \left( " + (LaTeX[k]) + "; " + (LaTeX[l]) + "  \right) $  "