menu   Home Answers Math Games Free Resources Contact Me  

It Depends on the Angle

My Basic Algebra Concepts class just started a brief chapter on favorite to teach!  We are currently working on angles, and as we went through the definitions, I noticed my students were having difficulty distinguishing complimentary from supplementary angles.  Since most of my students are visual learners, I had to come up with something that would jog their memory.

The definition states that complementary angles are any two angles whose sum is 90°.  (The angles do not have to be next to each other to be complementary.)  As seen in the diagram on the left, a 30° angle + a 60° angle = 90° so they are complementary angles.  Notice that the two angles form a right angle or 1/4 of a circle.

If I write the word complementary and change the first letter  "C" into the number nine and I think of the letter "O" as the number zero, I have a memory trick my mathematical brain can remember. 

Supplementary Angles are two angles whose sum is 180°.  Again, the two angles do not have to be together to be supplementary, just so long as the total is 180 degrees. In the illustration on your right, a 110° angle + a 70° angle = 180°; so, they are supplementary angles.  Together, they form a straight angle or 1/2 of a circle. 
If I write the word supplementary and alter the "S" so it looks like an 8, I can mentally imagine 180°.

 Since there are so many puns for geometric terms. I must close with a bit of geometry humor.

Having Fun With Angles

Want a variety of hands-on ideas on how to introduce angles to your students?
Check out this resource.