Triangle Inequality Theorem

Any side of a triangle must be shorter than the other two sides added together.

When one side is longer, the other two sides don't meet!

When one side is equal to the other two sides it is not a triangle
(just a straight line back and forth).

  triangle inequality 40 base, 16 and 22 cannot join

Try moving the points below:


When the three sides are a, b and c, we can write:

  • a < b + c
  • b < a + c
  • c < a + b