Math Fun Facts!
hosted by the Harvey Mudd College Math Department created, authored and ©1999-2010 by Francis Su
Subscribe to our RSS feed   or follow us on Twitter.
Get a random Fun Fact!
No subject limitations
Search only in selected subjects
    Calculus or Analysis
    Number Theory
    Other subjects
  Select Difficulty  
Enter keywords 

  The Math Fun Facts App!
  List All : List Recent : List Popular
  About Math Fun Facts / How to Use
  Contributors / Fun Facts Home
© 1999-2010 by Francis Edward Su
All rights reserved.

From the Fun Fact files, here is a Fun Fact at the Easy level:

Difference of Squares

You have all learned that

a2 - b2 = (a + b)(a - b)

But perhaps you haven't thought about how to use this to do fast mental calculations! See if you can guess how this trick can help you do the following in your head:

43 x 37
78 x 82
36 x 24

Let's do the first one. 43 x 37 = (40 + 3)(40 - 3) = 402 - 32 = 1600 - 9 = 1591.

Practice these, and you'll be able to impress your friends!

Presentation Suggestions:
See if the class can figure out what you are about to do.

The Math Behind the Fact:
The moral of the story is if you think CREATIVELY about everything that you learn in mathematics, even the easy stuff like algebra, you will find some surprising applications! See more Fun Facts on lightning arithmetic, or check out the reference below.

How to Cite this Page:
Su, Francis E., et al. "Difference of Squares." Math Fun Facts. <>.

Keywords:    lightning arithmetic, algebra
Subjects:    algebra
Level:    Easy
Fun Fact suggested by:   Francis Su
Suggestions? Use this form.
Click to rate this Fun Fact...
    *   Awesome! I totally dig it!
    *   Fun enough to tell a friend!
    *   Mildly interesting
    *   Not really noteworthy
and see the most popular Facts!
New: get the MathFeed iPhone App!

Brings you news and views on math:
showcasing its power, beauty, and humanity

Want another Math Fun Fact?

For more fun, tour the Mathematics Department at Harvey Mudd College!