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Show that each of these conditional statements is a tautology by using truth tables. a) \([\neg p \wedge(p \vee q)] \rightarrow q\) b) \([(p \rightarrow q) \wedge(q \rightarrow r)] \rightarrow(p \rightarrow r)\) c) \([p \wedge(p \rightarrow q)] \rightarrow q\) d) \([(p \vee q) \wedge(p \rightarrow r) \wedge(q \rightarrow r)] \rightarrow r\)

Short Answer

Expert verified
All given statements are tautologies as verified by truth tables.

Step by step solution

01

- Understand the Problem Statement

The goal is to prove that each conditional statement is a tautology. A tautology is a statement that is true in all possible scenarios. This can be determined using truth tables.
02

- Set Up Table for (a)

Create a truth table for \( [eg p \wedge(p \vee q)] \rightarrow q \). List all possible truth values for \(p\) and \(q\).
03

- Fill Truth Values for \( eg p \)

Fill out the column for \( eg p \). \[ \begin{array}{c|c|c} p & q & eg p \ \text{T} & \text{T} & \text{F} \ \text{T} & \text{F} & \text{F} \ \text{F} & \text{T} & \text{T} \ \text{F} & \text{F} & \text{T} \ \end{array} \]
04

- Fill Truth Values for \( p \vee q \)

Fill out the column for \( p \vee q \). \[ \begin{array}{c|c|c|c} p & q & eg p & p \vee q \ \hline \text{T} & \text{T} & \text{F} & \text{T} \ \text{T} & \text{F} & \text{F} & \text{T} \ \text{F} & \text{T} & \text{T} & \text{T} \ \text{F} & \text{F} & \text{T} & \text{F} \ \end{array} \]
05

- Fill Truth Values for \( eg p \wedge (p \vee q) \)

Fill out the column for \( eg p \wedge (p \vee q) \). \[ \begin{array}{c|c|c|c|c} p & q & eg p & p \vee q & eg p \wedge (p \vee q) \ \hline \text{T} & \text{T} & \text{F} & \text{T} & \text{F} \ \text{T} & \text{F} & \text{F} & \text{T} & \text{F} \ \text{F} & \text{T} & \text{T} & \text{T} & \text{T} \ \text{F} & \text{F} & \text{T} & \text{F} & \text{F} \ \end{array} \]
06

- Fill Truth Values for \( eg p \wedge (p \vee q) \rightarrow q \)

Fill out the column for the entire expression. The implication is true except when the antecedent is true and the consequent is false. \[ \begin{array}{c|c|c|c|c|c} p & q & eg p & p \vee q & eg p \wedge (p \vee q) & [eg p \wedge(p \vee q)] \rightarrow q \ \hline \text{T} & \text{T} & \text{F} & \text{T} & \text{F} & \text{T} \ \text{T} & \text{F} & \text{F} & \text{T} & \text{F} & \text{T} \ \text{F} & \text{T} & \text{T} & \text{T} & \text{T} & \text{T} \ \text{F} & \text{F} & \text{T} & \text{F} & \text{F} & \text{T} \ \end{array} \] Since all entries in the final column are true, the statement is a tautology.
07

- Repeat for (b)

Construct a truth table for \( [(p \rightarrow q) \wedge(q \rightarrow r)] \rightarrow(p \rightarrow r) \) and verify that all entries are true.
08

- Repeat for (c)

Construct a truth table for \( [p \wedge(p \rightarrow q)] \rightarrow q \) and verify that all entries are true.
09

- Repeat for (d)

Construct a truth table for \( [(p \vee q) \wedge(p \rightarrow r) \wedge(q \rightarrow r)] \rightarrow r \) and verify that all entries are true.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Truth Tables
Truth tables are a powerful tool used in propositional logic to systematically explore all possible truth values of logical expressions. They allow us to visualize how the truthfulness of propositions changes based on the combination of their individual components.
  • The table's rows represent all possible combinations of truth values for the given propositions.
  • Columns are added to evaluate intermediate expressions leading up to the final logical statement.
  • Each row is filled based on the logical operation defined in the statement.
Creating a truth table involves the following steps:

1. List all possible combinations of truth values for the involved propositions.
2. Calculate the truth value of each sub-expression.
3. Determine the truth value of the final expression for every possible combination of inputs.
By checking the final column of a truth table, we can see if a given statement is always true (a tautology), always false (a contradiction), or varies with different inputs.
Logical Implications
A logical implication is a type of conditional statement often represented as \( p \rightarrow q \). It states that if proposition \( p \) (the antecedent) is true, then proposition \( q \) (the consequent) must also be true.
  • The implication is true when both \( p \) and \( q \) are true.
  • It is also true when \( p \) is false, regardless of the truth value of \( q \).
  • The only time an implication is false is when \( p \) is true and \( q \) is false.
This might seem a bit counterintuitive, but it is based on a logical definition, and can be confirmed through truth tables. Such implications are foundational in mathematics and computer science for constructing proofs, algorithms, and conditional logic.
Propositional Logic
Propositional logic is the area of logic that deals with propositions, which are statements that can either be true or false. Instead of considering the underlying meaning of propositions, propositional logic focuses solely on their truth values and how they combine in logical expressions, using logical connectives:
  • Conjunction (\( p \wedge q \)) - True if both \( p \) and \( q \) are true.
  • Disjunction (\( p \vee q \)) - True if at least one of \( p \) or \( q \) is true.
  • Negation (\( eg p \)) - True if \( p \) is false.
  • Implication (\( p \rightarrow q \)) - True if either \( p \) is false or \( q \) is true.
  • Biconditional (\( p \leftrightarrow q \)) - True if \( p \) and \( q \) are both true or both false.
Propositional logic serves as the building block for more complex logical systems and is essential for a wide range of applications鈥攆rom daily reasoning to advanced mathematical proofs.
Conditional Statements
Conditional statements are fundamental constructs in logic and mathematics that express dependencies between propositions. They are typically written as \( p \rightarrow q \), where \( p \) is the condition (or antecedent) and \( q \) is the result (or consequent).
  • In conditional statements, the only scenario where the statement is false is when \( p \) is true and \( q \) is not.
  • In every other scenario (where \( p \) is false or \( q \) is true), the conditional is true.
To better understand the validity and truth value of conditional statements, you can use truth tables to test all possible truth values of the involved propositions.
Through exercises with conditional statements, you learn to see how complex logical constructs operate. This process helps in developing critical thinking skills and a deeper understanding of logical reasoning.

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