A

f(x) = x^(2)
a = -1.5 (slider from -3 to 3)
A: (a, f(a))
b: a + 2
B: (b, f(b))
m: (y(B) - y(A)) / (x(B) - x(A))
g(x) = (m * (x - a)) + f(a)
I = IntegralBetween(g(x), f(x), a, b)