The Unapologetic Mathematician

Mathematics for the interested outsider

The Integral Mean Value Theorem

Okay: time to get back on track. Today, we’ll see a theorem about integrals that’s similar to the Differential Mean Value Theorem. Specifically, it states that if we have a continuous function f:\left[a,b\right]\rightarrow\mathbb{R} then there is some c\in\left[a,b\right] so that

\displaystyle f(c)=\frac{1}{b-a}\int\limits_a^bf(x)dx

Let’s consider the Darboux sums we use to define the integral. We know that if we choose a partition, then its upper Darboux sum is greater than any Riemann sum of any refinement of that partition. So let’s take the absolute coarsest possible partition: the one where we just have partition points a and b. Then the upper Darboux sum is (b-a)M, where M is the maximum value of f on the interval \left[a,b\right]. Similarly, the lower Darboux sum on this interval is (b-a)m (where m is the minimum value of f), and it’s the lowest possible Darboux sum. Then we can divide everything in sight by b-a to get the inequality

\displaystyle m\leq\frac{1}{b-a}\int\limits_a^bf(x)dx\leq M

Now the Intermediate Value Theorem tells us that f must take every value between m and M at some point between a and b. And thus there must exist a c\in\left[a,b\right] so that

\displaystyle f(c)=\frac{1}{b-a}\int\limits_a^bf(x)dx

just as we wanted.

February 12, 2008 - Posted by | Analysis, Calculus


  1. This theorem is just a reformulation of the differential MVT if you take into account the fundamental theorem of calculus (exercise).

    Comment by Michael Livshits | February 13, 2008 | Reply

  2. Which theorem I have not yet covered. Patience, Michael. I know you know far better than I how I should be covering this material, but in the absence of your definitive weblog on the subject, I’m going through it in my own way.

    Comment by John Armstrong | February 13, 2008 | Reply

  3. […] now let’s use the Integral Mean Value Theorem to get at the integral here. It tells us that there’s some between and with — the […]

    Pingback by The Fundamental Theorem of Calculus I « The Unapologetic Mathematician | February 13, 2008 | Reply

  4. […] Mean Value Theorems We’ve got two different analogues of the integral mean value theorem for the Riemann-Stieltjes […]

    Pingback by Two Mean Value Theorems « The Unapologetic Mathematician | March 28, 2008 | Reply

  5. Great post! Very powerful theorems.

    Comment by Daily Calculus | April 9, 2008 | Reply

  6. […] Mean Value Theorem for Multiple Integrals As in the single variable case, multiple integrals satisfy a mean value […]

    Pingback by The Mean Value Theorem for Multiple Integrals « The Unapologetic Mathematician | December 29, 2009 | Reply

  7. […] Integral Mean Value Theorem We have an analogue of the integral mean value theorem that holds not just for single integrals, not just for multiple integrals, but for integrals over […]

    Pingback by The Integral Mean Value Theorem « The Unapologetic Mathematician | June 14, 2010 | Reply

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s


Get every new post delivered to your Inbox.

Join 412 other followers

%d bloggers like this: