2.
A truth table is a device used to determine when a
compound statement is true or false.
Truth Tables
3.
Formal Name Symbol Read Symbolic Form
Negation ~ “Not” ~p
Conjunction ∧ “And” p ∧ q
Disjunction ∨ “Or” p ∨ q
Conditional → “If p then q” p → q
Biconditional ↔ “If and only
if”
p ↔ q
Connectives used in truth
tables
7.
Let p represent the statement 4 > 1, q represent the
statement 12 < 9, and r represent 0 < 1. Decide
whether each statement is true or false.
a) ~p ∧ ~q
b) (~p ∧ r) ∨ (~q ∧ p)
Example: Mathematical
Statements
9.
Conjunction - both statements must be true
Two True T statements will result in a True T
-Any other combination will produce a False F.
Conjunction
11.
Let p represent the statement 4 > 1, q represent the
statement 12 < 9 find the truth of p ∧ q.
Solution
False, since q is false.
Example: Finding the Truth
Value of a Conjunction
12.
Disjunction - If either/or both statements are true,
the entire statement is true . One True T will result in
a True T statement; two False F statements will result in
a False F.
Disjunction
13.
p q p ∨ q
T T T
T F T
F T T
F F F
Truth table for disjunction
14.
Let p represent the statement 4 > 1, q represent the
statement 12 < 9 find the truth of p ∨ q.
Solution
True, since p is true.
Example: Finding the Truth
Value of a Disjunction
15.
Conditional
Conditional - only false if the second statement is
false and it follows a true statement. All other
combinations of True T and False F are True T.
16.
p q p → q
T T T
T F F
F T T
F F T
Truth table for conditional
18.
Solution
In Example 1, p represents, "I do my homework,"
and q represents "I get my allowance." The
statement p q is a conditional statement which
represents "If p, then q."
19.
Biconditional - true only if both statements are true
or both statements are false. All other combination of
the True T and False F are False F.
Biconditional
20.
p q p ↔ q
T T T
T F F
F T F
F F T
Truth table for
biconditional
21.
Example:
Given:
p: x + 2 = 7
q: x = 5
Problem:
Write p ↔ q as a sentence. Then determine its truth
values p ↔ q.
Example of a biconditional
statement
22.
Solution
The biconditonal p ↔ q represents the sentence:
"x + 2 = 7 if and only if x = 5." When x = 5, both p
and q are true. When x 5, both p and q are false.
A biconditional statement is defined to be true
whenever both parts have the same truth value.
23.
Equivalent Expressions
Equivalent expressions
are symbolic
expressions that have
identical truth values
for each corresponding
entry in a truth table.
Hence ~(~p) ≡ p.
The symbol ≡ means
equivalent to.
24.
Negation of the
Conditional
Here we look at the
negation of the
conditional.
Note that the 4th and 6th
columns are identical.
Hence p ^ ~q is
equivalent to ~(p q).
25.
The negation of the conjunction p ^ q is given by ~(p
^ q) ≡ ~p v ~q.
“Not p and q” is equivalent to “not p or not q.”
The negation of the disjunction p v q is given by ~(p v
q) ≡ ~p ^ ~q.
“Not p or q” is equivalent to “not p and not q.”
De Morgan’s Laws
26.
For any statements p and q,
~(p ∨ q) ≡ ~p ^ ~q and
~(p ^ q) ≡ ~p ∨ ~q
27.
Find a negation of each statement by applying De
Morgan’s Law.
a) I made an A or I made a B.
b) She won’t try and he will succeed.
Solution
a) I didn’t make an A and I didn’t make a B.
b) She will try or he won’t succeed.
Example: Applying De
Morgan’s Laws