Commutative Property of Multiplication

Pronunciation: /ˈkɒm yəˌteɪ tɪv ˈprɒp ər ti ʌv ˌmʌl tə plɪˈkeɪ ʃən/ ?

The commutative property of multiplication states that multiplying two numbers will get the same result no matter which number comes first.[1] The order in which two numbers are multiplied does not change the product. This is expressed by the equation: a·b = b·a.

cartoon showing a commuting to where b was
Figure 1: Commutative property of multiplication cartoon

One way to remember the commutative property of multiplication is to use the root word, 'commute'. Commute means to travel from one place to another, such as commuting to work. As diagrammed in figure 1, in the commutative property of multiplication, the variable 'a' commutes to where the 'b' was, and the variable 'b' commutes to where the 'a' was.

Commutative property of multiplication - a rectangle two dots high and three wide has the same number of dots as three high and two wide.
Figure 2 - Representation of 2·3 = 3·2 using dots.

Figure 2 is a representation of the commutative property of multiplication using dots. On the left is a rectangle showing 2·3. On the right is a rectangle showing 3·2. Both have six dots in them. You can transform the first into the second by turning the first on its side.

Sorry, the GeoGebra Applet could not be started. Please make sure that Java 1.4.2 (or later) is installed and active in your browser (Click here to install Java now)

Figure 3: Manipulative showing the commutative property of multiplication.

Figure 3 is a representation of the commutative property of multiplication that uses the length of a line segment to represent each number, and right angles to represent multiplication. Notice that when we 'multiply' one by the other, it doesn't matter which comes first, the total area is the same. Click on the yellow points of the two lines on top and drag the points. Dragging these points changes the diagram showing that, for any values of 'a' and 'b', this property holds true.

References

  1. commutative. merriam-webster.com. Encyclopedia Britannica. (Accessed: 2010-01-04). http://www.merriam-webster.com/dictionary/commutative.
  2. Jones, Burton. Elementary Concepts of Mathematics, pp 31-34. MacMillan and Company, 1947. (Accessed: 2010-01-12). http://www.archive.org/stream/elementaryconcep029487mbp#page/n52/mode/1up/search/commutative.
  3. Bettinger, Alvin K. and Englund, John A.. Algebra and Trigonometry, pg 2. International Textbook Company, January 1963. (Accessed: 2010-01-12). http://www.archive.org/stream/algebraandtrigon033520mbp#page/n18/mode/1up.
  4. Fine, Henry B., Ph. D.. Number-System of Algebra Treated Theoretically and Historically, 2nd edition, pg 5. D. C. Heath & Co., Boston, U.S.A., 1907. (Accessed: 2009-12-19). http://www.archive.org/stream/thenumbersystemo17920gut/17920-pdf#page/n14/mode/1up/search/commutative.

More Information

  • McAdams, David. Commutative. allmathwords.org. All Math Words Encyclopedia. Life is a Story Problem LLC. 2010-01-15. http://www.allmathwords.org/article.aspx?lang=en&id=Commutative.

Cite this article as:


Commutative Property of Multiplication. 2009-12-19. All Math Words Encyclopedia. Life is a Story Problem LLC. http://www.allmathwords.org/en/c/commutemult.html.

Translations

Image Credits

Revision History


2009-12-19: Added "References" (McAdams, David.)
2008-07-07: Changed manipulative from Geometer's Sketchpad to GeoGebra. Corrected spelling (McAdams, David.)
2008-03-25: Revised More Information to match current standard (McAdams, David.)
2007-07-12: Initial version (McAdams, David.)

All Math Words Encyclopedia is a service of Life is a Story Problem LLC.
Copyright © 2005-2011 Life is a Story Problem LLC. All rights reserved.
Creative Commons License This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 License