7. Logical Reasoning

7. LOGICAL REASONING
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LO:  SWBAT use logical reasoning to prove statements are true and find counterexamples to disprove statements that are false.
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Before we start, let's look at the format we will be using:

• Lower case letters will be used to name a statement.

 1. NEGATION

Negation is changing the truth value of a statement to its opposite value.  We designate the negated value with the symbol "~".

Example Statement:

p:  Austin is the capital city of Texas.    The truth value of this statement is True.  

~p:  Austin is NOT the capital city of Texas.  The truth value is now False.

Again, the ~p statement is the negated statement.

2. CONJUNCTION

A conjunction is a compound statement formed by joining two or more statements with the word and.  We then use the statements to write a compound statement.  (Compound just means mixing two things together in one). 

p:  Parallel lines have the same slopes

q:  Vertical angles are congruent

r:  The expression -5x + 11x simplifies to -6x

To write the compound statement, we use the symbol ∧.

So now we write our compound statements:

• p∧q (read as "p and q"):  Parallel lines have the same slope and vertical angles are congruent.
• ~p ∧ ~q (read as "not p and not q"):  Parallel lines DOES NOT have the same slope and vertical lines are NOT congruent.
• ~q ∧ r (read as "not q and r"):  Vertical angles are NOT congruent and the expression -5x + 11x simplifies to -6x.

3. DISJUNCTION

A disjunction is a compound statement formed by joining two or more statements with the word or.  We then use the the statements to write a compound statement.

Let's use the same statements from above

p:  Parallel lines have the same slopes

q:  Vertical angles are congruent

r:  The expression -5x + 11x simplifies to -6x

To write the compound statement, we use the symbol ∧.

So now we write our compound statements:

So now we write our compound statements:

• p∧q (read as "p and q"):  Parallel lines have the same slope or vertical angles are congruent.
• ~p ∧ ~q (read as "not p and not q"):  Parallel lines DOES NOT have the same slope or vertical lines are NOT congruent.
• ~q ∧ r (read as "not q and r"):  Vertical angles are NOT congruent or the expression -5x + 11x simplifies to -6x.

Note that the statements are identical except they are now joined by the word "OR" instead of "AND".

4.  TRUTH TABLES

We will fill in this table in class and discuss it.

5.  VENN Diagrams

We will examine the Venn Diagram and interpret data from it.

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Class Activity:

Handouts will be provided in class. 

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Homework:

P.87, questions 1 to 9.  The book is as below: