f(x)=-x²-6x+a

a = -3 (slider from -6 to 6, step 1)
f(x) = -x^(2.0) - 6.0 * x + a
A = Extremum(f)
b = OrthogonalLine(A, xAxis)
B = Intersect(b, xAxis)
c = Segment(A, B)
C, D = Intersect(f, xAxis)
d = Integral(f, x(B), 0.0)
text1: "f(x) = " + f
E = Intersect(f, yAxis)