C_f

f = Function(1.0 - x^(2.0), 0.0, 1.0)
a = 0.55 (slider from 0 to 1, step 0.01)
M: (a, f(a))
T_M = Tangent(M, f)
Q = Intersect(T_M, xAxis)
P = Intersect(T_M, yAxis)
O = Intersect(xAxis, yAxis)
poly1, j, a_1, i = Polygon(O, Q, P)