### 2.5 Postulates and Paragraph Proofs.notebook

```2.5 Postulates and Paragraph Proofs.notebook
Unit 3: Reasoning and Proof
2.5 Postulates and Paragraph Proofs
What is a
postulate?
September 10, 2013
Name
Geometry 4B
Date
in geometry - accepted as true
without proof
ex: The intersection of two lines is a point.
What is an
axiom?
a statement accepted as true
What is a
theorem?
a statement we can prove using
definitions, postulates and properties
ex: x = x
ex: Vertical angles are congruent.
What is a
proof?
logical argument used to prove
a statement is true
1
2.5 Postulates and Paragraph Proofs.notebook
September 10, 2013
2
2.5 Postulates and Paragraph Proofs.notebook
September 10, 2013
3
2.5 Postulates and Paragraph Proofs.notebook
September 10, 2013
4
2.5 Postulates and Paragraph Proofs.notebook
September 10, 2013
Explain Why:
If M is the midpoint of XY, then XM = MY.
Write your explanation in a short paragraph
(2 or 3 sentences)
5
2.5 Postulates and Paragraph Proofs.notebook
September 10, 2013
Steps to a Proof:
1) List the given information
2) List the statement you are proving
3) Create an argument
(a logical chain of statements
from the given info to the statement you are proving)
4) Provide reasons for your statements
(definitions, algebraic properties, postulates)
5) State what you have proven
6
2.5 Postulates and Paragraph Proofs.notebook
September 10, 2013
This is also in your book on page 129.
7
2.5 Postulates and Paragraph Proofs.notebook
September 10, 2013
Homework:
LOD and LOS Practice
p. 131 # 27­29
Write a paragraph proof for:
Given:
2 and 4 are vertical angles Prove: 2 4 1
2
3
4
8
2.5 Postulates and Paragraph Proofs.notebook
September 10, 2013
9
```