Math Problem Statement

Let P, Q, and R be three propositions. Use truth table to prove that   (P →Q) V R and ¬((P∧¬Q)∧¬R) are logically equivalent.

Solution

To prove that the propositions (PQ)R(P \to Q) \vee R and ¬((P¬Q)¬R)\neg((P \wedge \neg Q) \wedge \neg R) are logically equivalent, we'll create a truth table. The propositions are logically equivalent if the truth values of both expressions are the same for all possible combinations of truth values of PP, QQ, and RR.

Let's break down the two propositions:

  1. (PQ)R(P \to Q) \vee R

    • PQP \to Q means "if PP, then QQ", which is logically equivalent to ¬PQ\neg P \vee Q.
    • So, (PQ)R=(¬PQ)R(P \to Q) \vee R = (\neg P \vee Q) \vee R.
  2. ¬((P¬Q)¬R)\neg((P \wedge \neg Q) \wedge \neg R)

    • First, evaluate the expression inside the negation: (P¬Q)¬R(P \wedge \neg Q) \wedge \neg R.
    • Then, negate the whole expression.

Now let's create the truth table.

Truth Table:

PPQQRRPQP \to Q(PQ)R(P \to Q) \vee RP¬QP \wedge \neg Q(P¬Q)¬R(P \wedge \neg Q) \wedge \neg R¬((P¬Q)¬R)\neg((P \wedge \neg Q) \wedge \neg R)
TTTTTFFT
TTFTTFFT
TFTFTTFT
TFFFFTTF
FTTTTFFT
FTFTTFFT
FFTTTFFT
FFFTTFFT

Explanation:

  1. The column for PQP \to Q shows the truth values of the implication.
  2. The column for (PQ)R(P \to Q) \vee R shows the disjunction (OR) of PQP \to Q and RR.
  3. The column for P¬QP \wedge \neg Q shows when PP is true and QQ is false.
  4. The column for (P¬Q)¬R(P \wedge \neg Q) \wedge \neg R shows when both P¬QP \wedge \neg Q and ¬R\neg R are true.
  5. The final column shows the negation of the previous column.

As you can see from the truth table, the columns for (PQ)R(P \to Q) \vee R and ¬((P¬Q)¬R)\neg((P \wedge \neg Q) \wedge \neg R) are identical. Therefore, the two propositions are logically equivalent.


Would you like further details on how the truth table was constructed?

Here are five related questions:

  1. What is the meaning of logical equivalence in propositional logic?
  2. How do implications (PQP \to Q) behave when PP or QQ are false?
  3. Can you explain the De Morgan's laws and how they relate to negations?
  4. How do you prove two propositions are equivalent without a truth table?
  5. What are some practical applications of logical equivalence in computer science?

Tip: When creating truth tables, always double-check each step of the evaluation to ensure consistency across the columns.

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Math Problem Analysis

Mathematical Concepts

Propositional Logic
Truth Tables
Logical Equivalence
Negation
Implication

Formulas

P → Q ≡ ¬P ∨ Q
¬(A ∧ B) ≡ ¬A ∨ ¬B (De Morgan's Law)

Theorems

De Morgan's Laws
Logical Equivalence

Suitable Grade Level

Grades 10-12 (High School Level)