1. 2.2: An Introduction to Logic
Expectations:
L3.2.1: Know and use the terms of basic logic.
L3.2.2: Use the connectives “not,” “and,” “or,” and “if..., then,” in mathematical and everyday settings. Know the truth table of each connective and how to logically negate statements involving these connectives.
L3.2.4: Write the converse, inverse, and contrapositive of an “If..., then...” statement. Use the fact, in mathematical and everyday settings, that the contrapositive is logically equivalent to the original while the inverse and converse are not.
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2. Conditional Statements
“If I get an A on my test, then I get to go to Disneyworld.”
“If the sky is blue, then it is not raining.”
“If x2 = 16, then x = 4.”
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3. Conditional Statements
“If p, then q.”
p: _______________
q: _______________
“If” is NOT a part of the hypothesis and “then” is NOT part of the conclusion.
The hypothesis and conclusion are each complete sentences.
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4. Conditional Statements
Identify the hypothesis and conclusion for the statement below.
If I get all of my work done, then I get to play.
Hypothesis:
Conclusion:
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5. Conditional Statements
Logic Form
p q
“ p implies q”
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6. Conditional Statements
Write, “If x = 3, then x + 4 = 7,” in logic form.
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7. Other Forms of Conditionals
Instead of being written using the terms if and then, some conditionals are written using terms like, all, every and q if p.
All squares are rectangles.
Every fraction is a real number.
Angles are supplementary if they form a linear pair.
Vertical angles are congruent.
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8. 2.2: An Introduction to Logic
It can be very helpful to rewrite these other forms as if-then statements.
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9. Write the following in if – then form.
a. All squares are rectangles.
b. Every cat is a mammal.
c. We will not have school if we get 12 inches of snow.
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10. Conditional Statements
Venn (Euler) Diagrams for Conditionals
“If p, then q.”
p=>q
___ __
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12. Draw a Venn Diagram for:
If a student is a freshman (9th grade), then they are in high school.
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13. Write a Conditional Statement for:
A triangle is isosceles.
A triangle is equilateral.
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14. 2.2: An Introduction to Logic
Conditional Statement: p q.
Conditional statements as promises:
If p happens, then “I promise” q will happen.
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15. 2.2: An Introduction to Logic
Ex: If Trevor eats a good dinner, then he gets dessert.
If Trevor eats a good dinner, then I promise he gets dessert.
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Truth Value of Conditional Statements:
p q is false iff the promise is broken.
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17. 2.2: An Introduction to Logic
If I wash the car, then I get to go to the movies.
4 cases to consider:
1. I wash the car and I go to the movies.
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18. 2.2: An Introduction to Logic
2. I wash the car, but do not get to go to the movies.
3. I do not wash the car, but I go to the movies.
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19. 2.2: An Introduction to Logic
4. I do not wash the car and I do not get to go to the movies.
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20. Bellwork 9/29/2010
S is between A and B such that AS is 4 more than SB tripled. If AB = 52, what are the AS and SB?

21. 2.2: An Introduction to Logic
Truth Table for Conditionals.
p q
true true
true false
false true
false false
p q
Start 9/29
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22. 2.2: An Introduction to Logic
Converses
The converse of p q is ________.
p q: If x + 4 = 10, then x = 6.
q p: If x = 6, then x + 4 = 10.
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23. 2.2: An Introduction to Logic
Write a conditional with the hypothesis “a triangle is a right triangle” and the conclusion “it has a 90° angle.”
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24. 2.2: An Introduction to Logic
Write the converse of your conditional. Is it true or false?
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25. 2.2: An Introduction to Logic
Determine the truth value of the conditional below. Then write the converse and determine its truth value.
If M is the midpoint of AB, then AM = MB.
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Truth Table for Converses.
p q
true true
true false
false true
false false
q p
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29. ACT/PLAN Prep
When the point (4,-1) is reflected across the y-axis, what are the coordinates of its image?
(-4,-1)
(-4,1)
(-1,4)
(4,-1)
(4,1)

30. 2.2: An Introduction to Logic
Assignment 2.2.1
pages 95 – 98, 9 – 12 (all), 14 – 28 (evens)
Start 9/30
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31. Functional Equivalence
Two statements are said to be “logically equivalent,” “truth functionally equivalent” or simply “functionally equivalent” if there truth tables are identical. The tables must be in the same order.
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32. 2.2: An Introduction to Logic
Are conditional statements and their converses functionally equivalent?
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33. 2.2: An Introduction to Logic
Negation:
The nullifying of a statement.
The negation of statement p is not p, written ______.
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34. 2.2: An Introduction to Logic
Examples:
p: today is sunny
~p:
p: x = 4
~p:
p: Marcus is not late
~p:
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35. 2.2: An Introduction to Logic
A statement and its negation have __________ truth values.
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36. 2.2: An Introduction to Logic
Truth table for negations. p
true
false ~p
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37. 2.2: An Introduction to Logic
Inverse of a Conditional Statement:
The inverse of p q is __________.
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38. Write the inverse and determine the truth value of both statements.
p q : “If a quadrilateral is a square, then it is a rhombus.”
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39. 2.2: An Introduction to Logic
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40. Write the inverse and determine the truth value of both statements.
p q : “If a triangle is equilateral, then all of its angles are congruent”
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Truth Table for Inverses.
p q
true true
true false
false true
false false
~p ~q
~p ~q
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43. 2.2: An Introduction to Logic
Are conditionals and their inverses functionally equivalent?
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44. 2.2: An Introduction to Logic
Contrapositive of a Conditional Statement:
The contrapositive of p q is ___________.
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45. 2.2: An Introduction to Logic
Write the contrapositive and determine the truth value of both statements.
p q : If a quadrilateral is a square, then it is a rectangle.
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46. 2.2: An Introduction to Logic
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47. 2.2: An Introduction to Logic
Truth Table for Contrapositives.
p q
true true
true false
false true
false false
~p ~q
~q ~p
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48. 2.2: An Introduction to Logic
Are conditionals and their contrapositives functionally equivalent?
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49. 2.2: An Introduction to Logic
Are converses functionally equivalent to inverses?
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50. 2.2: An Introduction to Logic
Consider the following statement: “If m is an odd number, then m is not divisible by 2.” Which represents the contrapositive of the original statement? A. If m is divisible by 2, then m is an odd number. B. If m is divisible by 2, then m is not an odd number. C. If m is an odd number, then m is not divisible by 2. D. If m is not divisible by 2, then m is not an odd number.
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51. Transitive Property for Conditionals
If p q and q r, then ___________.
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52. Make a conclusion given the following statements:
If a triangle is equilateral, then it is isosceles.
If a triangle is isosceles, then it has at least 2 congruent angles.
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53. 2.2: An Introduction to Logic
Logic Chains
The transitive property can be extended past 2 statements to form a logic chain.
Ex: If a b, b c, c d, d e, e f, then _______.
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54. Using the following statements, what may you conclude?
If a polygon is a square then it is a rectangle.
If a polygon is a rectangle, then it is a parallelogram.
If a polygon is a parallelogram, then it is a quadrilateral.
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55. Using the following statements, what may you conclude?
If a quadrangle is a square then it is a rhombus.
If a quadrangle is a parallelogram, then it has exactly 2 pairs of parallel opposite sides.
If a quadrangle is a rhombus, then it is a parallelogram.
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56. Identify the statement that must be logically equivalent to the given statement.
“If a bird is a cardinal, then it is red.”
If a bird is not a cardinal, then it is not red.
If a bird is red, then it is a cardinal.
If a bird is red, then it is not a cardinal.
If a bird is not red, then it is a cardinal.
If a bird is not red, then it is not a cardinal.

57. 2.2: An Introduction to Logic
Assignment 2.2.2
pages 95 – 98,
#9 – 12 (all), 30, 32 and 51 – 53 (all)
Pages 788 – 790,
#10, 12, 14, 22 and 24
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