Friday, February 15, 2013

Function Composition Relay

I've taught function composition in Algebra II and in Pre-Calculus, and my students ALWAYS seem to struggle with it.  I remember it actually bringing a girl to tears in one of my first years of teaching.  So this year I decided to try and try a more informal approach to introduce the concept in hopes that it would make something "click" for my students.

I printed this out and cut apart the functions.

Function Composition Relay

Each person in a group got a different function.  Then I wrote on the board the definitions of composition (f (g(x)) and g(f(x))) and explained that it was like a relay, with the inside handing off to the outside.  I started with an example of composition on a number: f(g(2)) and explained that this meant that g would take the 2 and do "its thing" to the 2, then hand off the result to f and then f would do "its thing" and get the final result.  I posted several more examples of composition on a number on the board, one at a time, and had them calculate the results in their group.  We even did composition of three and even four functions.  Then I asked them "What if I want to know a formula for the relay so that I don't have to actually do the relay in order to figure out how it turns out?  In other words, what if I want to find the composition on x?"  We then did f(g(x)) together.  They were able to do any combination of function composition I put on the board, including (with a little help) the f(g(h(j(x)) composition.  It went great!  I will definitely be teaching composition as a relay from now on.

I will say that my students still struggled to recognize the symbol for composition when it showed up on the test.  If I reminded them that it was the "relay" operation, they would go "oh, yeah!", so I'm going to have to give them some more independent practice with the notation next year....

1 comment:

  1. Do you have a file or picture? All I can see is an empty white box? :(