61/2 A Closer Look at Proof
A)
How a Deductive System Works
a.
What are the three undefined terms of Geometry?
b.
How many postulates do we have?
c.
We build our definitions and theorems using these undefined
terms and postulates
i.
Ex) The distance PQ was defined to be the positive
number given by the Distance Postulate
ii.
Ex) a set of points is
collinear
if all points of the set lie on
the same
line
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
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 Spring '09
 Johnson
 Logic, Algebra, undefined terms, Distance Postulate Ex

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