Triangle Inequality Theorem
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Objective
I can determine if three side lengths form a triangle using the triangle inequality theorem.
Part 1 of 4
Warm-up video
Destress Math · 7:14
We don't generate video — this one is by Destress Math on YouTube. The practice questions and exit ticket below were drafted by AI for this objective, and every question is editable in the teacher guide.
Part 2 of 4
Key concepts
3 concepts
- 1
The triangle inequality theorem states that the sum of the two smaller sides of a triangle must be greater than the longest side.
- 2
To find the possible range for the third side of a triangle, you must subtract the two given sides to find the lower bound and add them to find the upper bound.
- 3
If given two sides of a triangle of lengths 7 and 5, the third side (x) must fall in the range 2 < x < 12.
Part 3 of 4
Practice
9 questions
Which of the following sets of side lengths CANNOT form a triangle?
Explain in your own words why the triangle inequality theorem works. Why must the sum of the two shorter sides of a triangle be greater than the longest side?
Part 4 of 4
Exit ticket
Quick comprehension check
“The lengths of two sides of a triangle are 8 cm and 10 cm. What is a possible length for the third side? Explain your answer.”
Sample answer included in the free materials
Get the materials
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Teacher Guide
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