## Monday, March 7, 2016

### Triangle Inequality Theorem

This is the second year I have taught the Triangle Inequality Theorem using spaghetti and I love doing it this way.

First I had students copy the table into their notebook and gave them a piece of spaghetti. Their instructions were to break it into three uneven pieces, measure the three pieces, and record their measurements under the columns short side, medium side, and long side. (I asked them to do three uneven pieces because last year too many students broke them into the exact same length and it was more difficult to illustrate the concept)
As the students were measuring, I was walking around the room asking students to write their measurements on the board. I looked for a mixture of those who lengths that would make a triangle and those who did not. I asked a few students to come to the board and share their triangle lengths.

BEFORE filling out the short + medium column, I ask students to try to make a triangle with their pieces. I asked the students who wrote their measurements on the board if their length pieces made a triangle and we added a "yes" or a "no" to the last column.

I didn't have the column labeled Short+Medium yet. So with 4/5 columns filled in, I asked the students to look for a pattern. Some classes were able to see that when two small side lengths were more than the large one, there was a triangle.

For the class that did not come to that conclusion, we added the short+medium, then added up those two sides and I asked them to look again.

It is one of my favorite lessons of the year. After we determined what the Triangle Inequality Theorem says, we put this foldable into the student notebooks.  My students did really well explaining when a triangle could be formed.

This foldable is now available in my store.