Transcript Notes Section 2.4

Geometry Notes
Section 2-4
What you’ll learn
How to use the Law of Detachment
 How to use the Law of Syllogism

Vocabulary
Deductive reasoning
 Law of Detachment
 Law of Syllogism

Deductive Reasoning
 DEFN
Deductive Reasoning:
An
argument that uses facts, rules,
definitions or properties to reach a
logical conclusion
Two basic forms of deductive reasoning
are:
 Law
of Detachment
 Law of Syllogism
Examples of Deductive Reasoning
First we need facts, rules, definitions or
properties to work with.
 Interesting Facts:
 All geometry students love TAB.
 KJ is a geometry student.
 What is a logical conclusion based on that
information?


KJ loves TAB.

Let’s build on our interesting facts. . .
Examples of Deductive Reasoning
Continued
 Interesting Facts:
 All geometry students love TAB.
 KJ is a geometry student.
 Any
new
Stacy
is aconclusions?
history student.
Nope.

Why not?
History student has
nothing to connect to

Let’s continue building our interesting facts.
Interesting Facts:
 All geometry students love TAB.
 KJ is a geometry student.
 Stacy is a history student.
 Geometry students who love TAB have
been known to steal one.
 Any new conclusions?
 What?


Let’s continue building our interesting facts.
Interesting Facts:
 All geometry students love TAB.
 KJ is a geometry student.
 Stacy is a history student.
 Geometry students who love TAB have
been known to steal one.
 KJ is a history student too .

Any new conclusions?
 Why not?


Let’s continue building our interesting facts.
Interesting Facts:
 All geometry students love TAB.
 KJ is a geometry student.
 Stacy is a history student.
 Geometry students who love TAB have
been known to steal one.
 KJ is a history student too.
 Students who steal TAB carry it in their
bookbag.
 Any new conclusions?
 What is it?

Interesting Facts:
 All geometry students love TAB.
 KJ is a geometry student.
 Stacy is a history student.
 Geometry students who love TAB have been
known to steal one.
 KJ is a history student too.
 Students who steal TAB hide it in their
bookbag.

Have you learned. . .
Or
did
we?
Hey! We
 How to use the Law of Detachment?
didn’t do
 How to use the Law of Syllogism?
these!

Assignment: Worksheet 2.4
Law of Detachment

Given p→q and p as true therefore q must
be true.
p→q
p

  q

What part of our argument illustrates the
Law of Detachment?
Law of Syllogism

Given p→q and q →r as true therefore
p→r must be true.
p→q
q →r

  p→r

What part of our argument illustrates the
Law of Syllogism?