Friday, December 13, 2013

Domain & Range from a Graph

My students have never had such accuracy in identifying domain and range from a graph.

Thanks to this little unsuspecting guy.

I blindfolded him and gave him eyes on the sides of his head.

And then he took a stroll across the x-axis to find to find domain.

Now the x-values that are included in the domain can be determined by stating the x-values where our little friend can "see" the graph.

Can he see it here? No.

What about here? No.

What is the smallest x-value where he can see the graph?  -9

Can he see it here? Yes

What is the largest x-value where he can see the graph? 9

So the domain is [-9, 9]

To find range, he strolls up the y-axis.

For a function that doesn't have endpoints, we talked about what the function looks like beyond the plane that is shown. Students really didn't have trouble with this.

All this silliness is the result of desperation.

For the first time ever, I am teaching two levels of Algebra 2. I am finding that some of my "standard" explanations aren't working with the "not advanced" group.

So then I'm all "Okay, that didn't work. Here, let me grab this toy bug from my closet." And stuff like this happens.


  1. I LOVE this! This was one of our first topics of the year in Algebra 2, and I still have students who never quite got it. I will definitely be trying something like this with them when we review for the semester test! Thanks for sharing!

    1. You are very welcome. I am glad it was helpful!

  2. I think that is a great lesson! Way to make it fun for them!

  3. This is great! I am definitely going to use this!

    1. Thank you, Lisa! I am happy you can use it. :)