1. Bell Ringer 9/13
How many diagonals can be formed in a 13 sided polygon?
(n)(n-3) 2
(13)(10)
= 65 2

2. Geometry

3. Today Goals Finding patterns
What does invariant mean?
invariant is something that does not
change under a set of transformations.
Finding patterns
Making generalizations from concrete examples
Identifying invariants
so something that stays constant.

4. Discovering the Δ Inequality Theorem
Form a triangle with 4 in. 5 in. & 8 in. straws.
Is it possible?
2) Copy the data sheet into your notes
3) Try the following lengths from the data sheet and fill in the table.
4) Answer the two questions from the data sheet into your notes.

5. Get ready for………….. 3 pieces do form a triangle
3 pieces does not form a triangle

6. Can we generalize anything here about the lengths of the sides of a triangle
Lets discuss

7. Get to the point
Go ahead and summarize what you have discovered. (One or two sentences)
The sum of any two sides of a triangle must be greater than the length of the third side.

8. Triangle Inequality Practice Problems
Class / Homework ..

9. On your paper
Copy this chart & find me three different examples which have sides lengths that form a triangle. Use a ruler to measure each straw length. (You may need to trade straw pieces with a partner to have enough different sized pieces).

10. Continue on your paper
Now find me three different examples which have sides lengths that DO NOT form a triangle.