Add the two smallest sides. If sum > largest side → triangle.
If you see a diagram with an extended side, remember that the "outside" angle will always be larger than the two "inside" angles that aren't touching it. This is a common "trick" question on Lesson 4.3 worksheets to test your conceptual understanding of triangle properties. Summary Checklist for Success lesson 4.3 triangle inequalities worksheet answers
5, 9, 14 Check: (5 + 9 > 14)? (14 > 14) → No (must be greater, not equal) Answer: No Add the two smallest sides