Triangle Inequality Theorem

Standard:

MA.8.GR.1.3 Use the Triangle Inequality Theorem to determine if a triangle can be formed from a given set of sides. Use the converse of the Pythagorean Theorem to determine if a right triangle can be formed from a given set of sides.

Triangle Inequality Theorem

I can calculate the missing side length of a triangle when given two sides using the Triangle Inequality Theorem.

Here are the rules about triangles:

• ALL angles need to add up to be 180 degrees! No matter what!

• The 3rd side of a triangle needs to be smaller than the sum of your two shorter sides.

• If you do not meet either of these rules, IT ISN'T A TRIANGLE!

Example:

I have the sides 2 ft, 2 ft, and 4 ft.

Add your two shortest sides: 2 + 2

2 + 2 is 4. Is my third side smaller than 4?

NO! This will not be a triangle. A good option for a 3rd side could be 3 ft or 2 ft. 4ft is too wide!