3rd Angle Of A Triangle Proof
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About this Lesson
 Type: Video Tutorial
 Length: 10:06
 Media: Video/mp4
 Use: Watch Online & Download
 Access Period: Unrestricted
 Download: MP4 (iPod compatible)
 Size: 111 MB
 Posted: 07/22/2010
This lesson is part of the following series:
Combined Beginning Algebra and Geometry Series (30 lessons, $19.80)
Geometry Help (19 lessons, $9.90)
It's fairly obvious that if two angles of one triangle are congruent to two angles of another triangle, then the third angles are congruent. However, how to write the proof may not be so obvious. For that matter, how to write ANY proof may not be so obvious!
That is probably the understatement of the world! Most students find proofs to be very difficult. This video "illustrates" a proof but doesn't really teach you how to write a proof. That will need a video all it's own! Coming soon.
For now, the most important part of this video is to get the concept of the 3rd angle...and, thank goodness, that IS very easy to get.
Learn this theorem. Do not worry if you cannot write the proof as I did. Try to follow me though. At this stage, being able to just follow my proof is enough. The concept is important to know. The proof...just follow me for now.
About this Author
 Sandra Wilkes
 30 lessons
 Joined:
07/05/2010
Welcome! I'm so glad you are here! Math help is here for you when you need it.
I believe that using these Algebra and Geometry videos will help you understand the basics of Algebra and Geometry.
Some students try very hard and still struggle to pass math. They start off strong but things quickly begin to fall apart. That happens as soon as the student becomes lost. Teenagers who find themselves in this position often let it "get away from them" before they seek help. Because Math is always a class of stepping stones, it rarely gets better without help.
I urge you to seek help from your child's teacher first. Always. These Algebra and Geometry videos can help too. You can watch...
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Lesson Outline:
A. Example Of A Proof
B. You cannot prove that something is true until you know that it is true in your own mind.
C. Every step must have a reason.
D. Reasons are definitions, postulates, or theorems.
E. No guessing when writing a proof.
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I seriously can't do proofs. But this is good and I am getting better at it. I wish you lived next door to me!