Download conditionals

2.5:If-Then Statements &
Deductive Reasoning
If you pay attention to this
lesson, then you will
understand it.
If-Then Examples
• If you live in New Jersey, then
you live in the U.S.
• If you add two even numbers,
then the sum is an even number.
• Today is my birthday if today is
July 29th.
If-Then Facts
• If-Then statements are called
Conditional Statements
• The part of the statement after
“if” is the Hypothesis
• The part of the statement after
“then” is the Conclusion
Color the hypothesis red and
the conclusion blue
• If you live in New Jersey, then
you live in the U.S.
• If you add two even numbers,
then the sum is an even number.
• Today is my birthday if today is
July 29th.
Now Its Your Turn!
Create two conditional
statements (one that is
true, and one that is
false). Identify the
hypothesis and
conclusion
Theorems and Postulates are usually
written in If-Then Form
• If 2 angles form a linear pair, then they
are supplementary.
• If 2 angles are vertical, then the two
angles are congruent.
Inductive vs. Deductive Reasoning
• Inductive Reasoning: conclusions
based on patterns (not always true)
• Deductive Reasoning: conclusions
based on facts, definitions, laws of
logic (always true)
2 Laws of Logic:
• 1) Law of Detachment: If the
hypothesis is true, then the conclusion
is true.
• 2) Law of Syllogism: Eliminate the
common conclusion/hypothesis.
Law of Detachment:
• If you buy a slice of pizza, then you
spent $2.00.
• Andrew bought a slice of pizza
• Therefore, Andrew spent $2.00
Law of Syllogism
• If Theresa plays volleyball, then she
will score a goal. If Theresa serves a
kill, then she will be happy.
• Theresa plays volleyball
• Therefore, Theresa will be happy