Triangle Inequality Theorem - Discovering Properties of Triangle Side Lengths:
Start out the lesson by saying “Ok, we are working with triangles, so before we start today, I need everyone to quickly move the desks to be arranged in one big triangle. Then we can begin. Please start with 16 (or an appropriate number that is slightly more than half of the number of desks in your classroom) of the desks in one straight line facing the front wall, and quickly slide the rest forward to complete a triangle off of that row.”
Students will start this process and realize that they do not have enough desks left over to complete the triangle. This can lead into a very brief discussion of the fact that some sets of three side lengths cannot make a triangle.
Then, hand out the worksheets and have students use manipulatives to begin the discovery activity. (It works well with students working in pairs.) Markers with caps that fit onto the base work perfectly as manipulatives, because they snap together to create rigid sides. You can also use toothpicks. Each student or pair will need about 12 pieces to work with.
Students will be led to discover the Triangle Inequality Theorem for themselves.
Here's what is included:
- two versions of the discovery worksheet (one with less guidance)
- "hint cards" for the teacher to offer to students who get stuck
- practice worksheets to follow up the activity
- directions and answer keys
***NOTE - This item is also included in a larger DISCOUNTED bundle: Triangles Bundle
You might also like these other resources:
Triangle Sum Theorem Inquiry Activity
Right Triangles & Trigonometry: "Choose Your Own Journey" Book
Similar Triangles Proofs