Triangle Inequality
A triangle forms only when the sum of any two side lengths is greater than the third side.
Do this: Read the concept below, then try the quiz or activity.
Lesson 146 of 190
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Concept
Triangle inequality conditions: For sides a, b, c: - a + b > c - a + c > b - b + c > a
If any condition fails, no triangle exists.
Example: 3, 4, 8 -> 3+4=7 not greater than 8, so not a triangle.
Example: 5, 6, 8 -> all pair sums exceed third, so triangle exists.
Try it
Decide if each set can form a triangle: 1. 4, 5, 9 2. 7, 10, 12 3. 3, 3, 5 4. 6, 14, 7 5. 9, 11, 18 6. Give one possible third side if two sides are 6 and 8.