## 2.18.2015

### Triangle Inequality Skewers

Fun times in Geometry right?

In the past I've done the Triangle Inequality Theorem with pipe cleaners and straws. Pipe cleaners = fail because student just bend them to make a triangle. Straws didn't work because 1) students cut them and 2) they are too wide.

I came up with bright idea of wooden skewers and did you know that in February I had to go to 4 different stores to find any? Random.

I used Sharpies to color code the different lengths and needle nose pliers >>>> scissors.

I modified Mrs. Hester's INB page Creating Triangles to fit my lengths since she used AngLegs.

I gave students a post-it and asked them to measure each color first.

Then they arrange and filled in the chart.

A problem I always have is when the a + b equals the c. For example, the 2 inch, 3 inch, and 5 inch sticks. I always have half of the class argue that they make a triangle and half that say they do not. I even showed them how they fold down and make a straight line but some were still not convinced. So it ended up with me telling them this is the way it is even though their experience told them different.

Any suggestions? I guess I can attribute it to my lack of cutting skills and order some AngLegs for next year,

1. I do this with the AngLegs, and we have that discussion too. I have made the rule that to be a triangle, it has to lay flat, have area, and be snapped together. The a+b=c case will only have area when they bend it- thus, it's not a triangle. I don't know exactly how that would work for the skewers, but it seems like the fact that it has to have enclose area might help.

1. But some of them really did seem to make triangles! There's a lesson on Geogebra where it turns purple when it makes a triangle but I feel like there is more meaning in physically making it with your hands. Guess I'll just have to order some AngLegs!

2. I did this with spaghetti noodles and have the same issue! I like the idea of the skewers because you can use them year to year (and class to class!) and it cuts the cutting and coloring time.

1. If I can't reuse it or make the students cut it then it's not happening for me! :)

3. I like using spaghetti because it's cheap, every student gets at least one, and they can just throw them away when they're done. I'll admit, though, that I haven't had any kids argue with me about equal lengths.

1. It's probably just my poor cutting skills. =)

4. Which colours represent which lengths?

1. Silver 8
Pink 7
Yellow 5
Orange 4
Green 3
Blue 2

5. Try doing this lesson for easy prep! http://7thgrademathteacherextraordinaire.blogspot.com/2014/07/triangle-inequality-theorem-ccss-7g2_8.html