How to Do Triangle Geometry Proofs

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Doing triangle geometry proofs will usually involve what are known as two column proofs. Do triangle geometry proofs with help from a professional private tutor in this free video clip.

Part of the Video Series: Math Made Easy
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Video Transcript

Hi, I'm Rachel, and today we're going to be going over how to do triangle proofs in geometry. So when we talk about doing these proofs we're usually talking about two column proofs and we usually want to prove if two triangles are congruent or if we know the triangles are congruent we're going to try and prove that the angles or the sides are congruent. So we usually use things like side side side, which we just abbreviate like this. Side, angle, side, which we abbreviate like that. Angle, angle, side and hypotenuse leg theorem. I like to think of it like there's no curse words if you ever try and think of maybe there's angle, side, side. There's not. You're never going to abbreviate with anything that can be a curse word. Those are all four things that we can use. So let's say we have two triangles that we want to prove are congruent. You're not sure because this is a poorly drawn picture, right. But you're usually given something, right, like say you're given that B and C are congruent sides and you know that maybe BCD right is bisected by AC. Well when you know that this is bisected then you know that these two angles are congruent to each other because an angle bisector bisects in to two separate equal parts. So you can start realizing you can use those two givens, this given and these two sides are equal and the given that this bisects to find that you can use side, angle, side. You have a side that's even, you have angles that are even right when you can prove it with the angle bisector, and then you can use the reflexive property to prove that AC equals AC and therefore prove that triangles ABC and ADC are congruent with side, angle, side. I'm Rachel and thanks for learning with us today.


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