Post on 06-Jan-2016
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Undefined Terms and Definitions 2-2A
Why do we need undefined terms?
What is a plane?
What is a biconditional statement?
Undefined terms
Name two undefined terms that we simply “understand”.
Point
Line
Third Undefined Term
Plane: a flat surface that extends infinitely. It has infinite length and width, but has not thickness.
A plane is named by a single capital letter.
P
Definition
Coplanar points:
points that lie in the same plane.
A
B
C
D
P
Noncoplanar points
Points that do not lie on the same plane.
AB
C
D
P
Q
Critical Attributes
Turn to page 109 in your book.
What Makes a Midpoint?
Turn to the Explore on page 110.
Definition of Biconditional Statement
When both a conditional and its converse are true, they are combined into one statement using the connector phrase “if and only if”.
“if and only if”
Definition
Point M is the midpoint of AB if and only if it divided AB into two congruent segments, AM and MB.
A BM
Both of the following statements are true.
• If M is the midpoint of AB, then it divides AB into two congruent segments.
• If a point M divided AB into two congruent segments, then it is the midpoint of AB.
A BM
Assignment 2-2A
Page 111, 1-6, 9-12, 19, 20