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Show that each conditional statement in the Exercise 10 is a tautology without using truth tables.

Short Answer

Expert verified

For showing the given conditional statements are tautologies, it is proved that the outcome of these statements in a truth table contains only Tvalue.

Step by step solution

01

Definition of Tautology  

Atautology is a compound statement that is true for all feasible truth values of the statements.

02

To Show conditional statement is a tautology without using a truth table

(a) [¬p(pq)]q

For showing, a given conditional statement is a tautology, prove that

[¬p(pq)]q=T

Follow the rule of logical equivalence

[¬p(pq)]q=¬[¬p(pq)]q

Follow De Morgan’s law

[¬p(pq)]q=[¬(¬p)¬(pq)]q

Follow double negation law

[¬p(pq)]q=[p¬(pq)]q

Follow De Morgan’s law

[¬p(pq)]q=[p(¬p¬q)]q

Follow distributive law

[¬p(pq)]q=[(p¬p)(p¬q)]q

Follow negation law

[¬p(pq)]q=[T(p¬q)]q

Follow commutative law

[¬p(pq)]q=[(p¬q)T]q

Follow identity law

[¬p(pq)]q=(p¬q)q

Follow associative and commutative law

[¬p(pq)]q=p(q¬q)

Follow negation law

[¬p(pq)]q=pT

Follow domination law

[¬p(pq)]q=T

Therefore, the conditional statement [¬ppq)]q is a tautology as it equivalent to

T

03

To Show conditional statement is a tautology without using a truth table

(b) [(pq)(qr)](pr)

For showing, a given conditional statement is a tautology, prove that

[(pq)(qr)](pr)

Follow the rule of logical equivalence

[(pq)(qr)(pr)=[(¬pq)(¬qr)](¬pr)[(pq)(qr)(pr)=¬[(¬pq)(¬qr)](¬pr)

Follow De Morgan’s law twice and the double negation law

[(pq)(qr)](pr)=[(¬pq)¬(¬qr)(¬pr)[(pq)(qr)](pr)=[(p¬q)(q¬r)(¬pr)

Follow distributive law twice

[(pq)(qr)](pr)=[(pq(p¬r))((¬qp)(¬q¬r))](¬pr)

Follow negation law and commutative law

[(pq)(qr)](pr)=[(pq(p¬r))(T(¬q¬r))](¬pr)

Follow identity law

[(pq)(qr)](pr)=[((pq)(p¬r))((¬q¬r))](¬pr)

Follow commutative and associative law

[(pq)(qr)](pr)=[(pq)(¬q¬r)(p¬r)](¬pr)

Follow commutative law and domination law

[(pq)(qr)](pr)=[(pq)(¬q¬r)(¬pr)]vT

Follow identity law

role="math" localid="1668241157691" [(pq)(qr)](pr)=[((pq)(¬q¬r))(¬pr)]

Follow distributive law

[pq(qr)](pr)=[(pq)(¬pr)((¬q¬r)(¬pr))]

Follow Commutative law and associative law

role="math" localid="1668241646783" [(pq)(qr)](pr)=[((p¬q)(qr))((¬q¬p)(¬rr))]

Follow negation law and commutative law

[pq(qr)](pr)=[T(qr)(¬q¬pT)]

Follow domination law

[pq(qr)](pr)=TT

Follow identity law

[pq(qr)](pr)=T

The conditional statement [pq(qr)](pr) is a tautology as it equivalent to

T.

04

To Show conditional statement is a tautology without using a truth table

(c) [p(pq)]q

For showing, a given conditional statement is a tautology, prove that

role="math" localid="1668242496181" [p(pq)]q=T

Follow the rule of logical equivalence

[ppq]q=[p¬pq]q

Follow De Morgan’s law

[p(pq)]q=[p¬p(pq)]q

Follow negation law

[p(pq)]q=[F(pq)]q

Follow identity law

[p(pq)]q=(pq)q

Follow the rule of logical equivalence

[p(pq)]q=(pq)(¬qq)

Follow negation and commutative law

[p(pq)]q=(pq)T

Follow domination law

[p(pq)]q=T

The conditional statement [p(pq)]q is a tautology a tautology as it equivalent to T

05

To Show conditional statement is a tautology without using a truth table

(d) [(pq)(pr)(qr)]r

For showing, a given conditional statement is a tautology, prove that

[(pq)(pr)(qr)]r

Follow the rule of logical equivalence

[(pq)(pr)(qr)]r=[(pq)(¬pr)(¬qr)]r

Follow distributive law

(pq)(pq)=[(pq)((¬p¬q)r)]r

Follow the rule of logical equivalence

(pq)(pq)=¬[(pq)((¬p¬q)r)]r

Follow De Morgan’s law thrice and the double negation law

(pq)(pq)=¬[(pq)¬((¬p¬q)r)]r(pq)(pq)=[(¬p¬q)(¬(¬p¬q)¬r)]r(pq)(pq)=[(¬p¬q)((pq)¬r)]r

Follow distributive law

role="math" localid="1668248271303" (pq)(pq)=[((¬p¬q)(pq))((¬p¬q)¬r)]r

Follow commutative and associative law

(pq)(pq)=[((¬pp)(¬qq))((¬p¬q)¬r)]r

Follow negation law

(pq)(pq)=[(T(¬qq))((¬p¬q)¬r)]r

Follow domination law

(pq)(pq)=[T((¬p¬q)¬r)]r

Follow identity law

(pq)(pq)=[((¬p¬q)¬r)]r

Follow distributive law

(pq)(pq)=[((¬p¬q)(¬rr))]

Follow negation and commutative law

(pq)(pq)=[((¬p¬q)T)]

Follow domination law

(pq)(pq)=T

The conditional statement(pq)(pq)is a tautology as it equivalent to T

Therefore, all the given conditional statements are tautologies.

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Most popular questions from this chapter

Which of these are propositions? What are the truth values of those that are propositions?

a) Do not pass go.

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c) There are no black flies in Maine.

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Let P(x),Q(x),and R(x)be the statements “xis a clear explanation,” “xis satisfactory,” and “xis an excuse,” respectively. Suppose that the domain for x consists of all English text. Express each of these statements using quantifiers, logical connectives, and P(x),Q(x),and R(x).

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d) Does (c) follow from (a) and (b)?

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Let p, q, and r be the propositions

p : Grizzly bears have been seen in the area.

q : Hiking is safe on the trail.

r : Berries are ripe along the trail.

Write these propositions using p, q, and r and logical connectives (including negations).

a)Berries are ripe along the trail, but grizzly bears have not been seen in the area.
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e) For hiking on the trail to be safe, it is necessary but not sufficient that berries not be ripe along the trail and for grizzly bears not to have been seen in the area.
f ) Hiking is not safe on the trail whenever grizzly bears have been seen in the area and berries are ripe along the trail.

Let p and q be the propositions p : It is below freezing. q : It is snowing. Write these propositions using p and q and logical connectives (including negations).

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d) It is either snowing or below freezing (or both).
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