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# Introduction to Proofs Fall 2013 with Answer Key (Editable)

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This worksheet is designed to replace a lecture on the topic of introducing students to geometric proofs.

I start out class with a 15-minute "mini-lesson," giving my students some basic examples of what today's lesson will be about. Once the mini-lesson is over, I have them get to work within their groups on this worksheet.

This worksheet covers the basics of proofs: setting up a T-chart with statements and reasons, the addition property of equality, the multiplication property of equality, the subtraction property of equality, and the division property of equality. It starts students doing algebraic proofs, since most are familiar with the basic steps required for algebra.

Then it moves onto basic geometric principles used in geometry: the reflexive property, the symmetric property, the transitive property, postulates such as the angle addition postulate, and the segment addition postulate. (Students are already familiar with these postulates, but they have not used them in proofs up until this point in time.)

Disclaimer: I take what I consider reasonable "shortcuts" by combining two or three "baby steps" in one. For instance, if I divide both sides of an equation by the same amount, and simplify the result, I call that entire process the division property of equality, whereas a more formal teacher may break it into several, smaller "baby steps." I made this decision based on my years of observing students struggle to get started with proofs, and I feel it is pedagogically appropriate to do so in this introductory exercise.

I use this activity within cooperative groups, and I circulate to make sure they are getting the purpose of the questions.

The file includes spiral review problems.

This worksheet is intended to be written on directly.

Please download the pdf preview file first, so you can see exactly what's included; the product file is a word document, which you may personalize for your students.
Immediately before this worksheet, I use the worksheet named 'Constructions Day 1: Duplicate Segments, Duplicate Angles, Midpoints with key' (http://www.teacherspayteachers.com/Product/Constructions-Day-1-Duplicate-Segments-Duplicate-Angles-Midpoints-with-key-366694), and immediately after this worksheet, I use the worksheet named 'Constructions Day 2 Fall 2013' (http://www.teacherspayteachers.com/Product/Constructions-Day-2-Fall-2013-1082528)

Keywords: Jonnard
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Teaching Duration
1 hour
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