f(x) = x^(2.0) / 4.0 + 2.0
b = 2
n = 7 (slider from 0 to 100, step 1)
a = 0
L = LowerSum(f, a, b, n)
U = UpperSum(f, a, b, n)
I = Integral(f, a, b)
IApprox: (L + U) / 2.0