# Part 3: Prove

**Strategy**
You observed the given diagram, then made a conjecture. Then you built a model and gathered some data. That may have caused you to rethink your conjecture somewhat--or perhaps it strengthened your conviction. Either way, by this phase you should have a conjecture that you truly believe in. The goal now is to demonstrate or *prove* your conjecture.
Does measuring angles prove whether or not angles are congruent? What does?
You can use any geometric tools, working on paper and/or in geogebra to try and find a way of demonstrating your conjecture.
**Two-Column Proof
**Now you've developed a way to demonstrate that your conjecture is true. A proof is how you clearly present your solution.
It begins with the problem as it is *given* to you. From there, you take one logical step at a time towards the conclusion you want to show is true. In this case, the conclusion you want to prove true is your conjecture.
Complete the proof in two-column form.