Integral definida
Author: Proyecto Algaida

n = 9 (slider from 0 to 300, step 1)
a = -2
b = 6
f(x) = x² / 4 + 2
c = LowerSum(f, a, b, n)
d = UpperSum(f, a, b, n)
F = Integral(f)
T1: "Suma superior: S  = " + d
T2: "Suma inferior: s  = " + c
e = Integral(f, a, b)
T3: "" + c + "   <  \int_{a }^{ b} f(x) dx   =  " + e + "   <   " + d
g: F(b)
h: F(a)
T4: "Regla de Barrow: F(b) - F(a) = " + g + "  -  ( " + h + " )  = " + (g - h)
T5: "S - s  =  " + d + "  -  " + c + "  =  " + (d - c)
T6: "s  <   \int_{a }^{b }  f(x) dx   =  " + e + " <  S "