f(x)=a(x-h)²+k

a = -0.8 (slider from -20 to 20, step 0.1)
h = -1 (slider from -20 to 20, step 0.1)
k = 13.4 (slider from -20 to 20, step 0.1)
f(x) = (a * (x - h)^(2)) + k
S = Extremum(f)
texte1 = LaTeX(f, true, true)
x_1, x_2 = Intersect(f, xAxis)