Triangle Inequality Theorem. The sum of the lengths of any two sides of a triangle is greater than the length of the third side.
According to the first triangle inequality theorem, the lengths of any two sides of a triangle must add up to more than the length of the third side. This means that you cannot draw a triangle that has side lengths 2, 7 and 12, for instance, since 2 + 7 is less than 12.
