Example 1: Find the average value of f(x) = x^2 from x = 2 to x = 4.
Evaluate the integral x^2 dx.
Example 2: Find the average value of f(x) = sin x on [0, π].
Evaluate sin x dx.
sin x dx = (−cos x) (−cos π + cos 0) =
The Second Fundamental Theorem of Calculus
As you saw in the last chapter, we’ve only half-learned the theorem. It has two parts, often referred to as
the First and Second Fundamental Theorems of Calculus.
The First Fundamental Theorem of Calculus (which you’ve already seen):
If f(x) is continuous at every point of [a, b], and F(x) is an antiderivative of f(x) on [a, b], then
f(x) dx = F(b) − F(a).
The Second Fundamental Theorem of Calculus:
If f(x) is continuous on [a, b], then the derivative of the function F(x) = f(t) dt is
f(t) dt = f(x)
We’ve already made use of the first theorem in evaluating definite integrals. In fact, we use the first
Fundamental Theorem every time we evaluate a definite integral, so we’re not going to give you any