f(x) = x^(2)
t = 0.3 (slider from -4 to 4, step 0.1)
A: (t, f(t))
h = 1 (slider from 0.01 to 1, step 0.01)
B: (t + h, f(t + h))
C: (t - h, f(t - h))
多角形1, c, a, b = Polygon(A, B, C)
d = Circle(A, B, C)
D = Center(d)