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Unformatted text preview: 61/2 A Closer Look at Proof
A) How a Deductive System Works a. What are the three undefined terms of Geometry? How many postulates do we have? We build our definitions and theorems using these undefined terms and postulates
i. b. c. Ex) The distance PQ was defined to be the positive number given by the Distance Postulate Ex) a set of points is collinear if all points of the set lie on the same line ii. B) Indirect Proof a. Supposition i. Opposite of the statement that you are trying to prove
1. use the supposition and continue your argument until reaching a contradiction It is frequently used when the statement you're trying to prove contains "not" 2. ii. Example 1. "It must not be raining outside."
a. iii. If it were raining, then those people coming in the door would be wet, but they aren't Example 1. "Today must not be the right day for the football game"
a. If the game were being played today, then by now the stadium would be full of people, but you and I are the only ones here ...
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This note was uploaded on 05/16/2011 for the course ALGEBRA 098 taught by Professor Johnson during the Spring '09 term at Grand Valley State University.
 Spring '09
 Johnson
 Algebra

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