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JEE Main 2022
Mathematical Reasoning
Mathematical Reasoning
Medium

Question

Among the statements (S1) : (pq)((p)q)(p \Rightarrow q) \vee((\sim p) \wedge q) is a tautology (S2) : (qp)((p)q)(q \Rightarrow p) \Rightarrow((\sim p) \wedge q) is a contradiction

Options

Solution

Key Concepts and Formulas

  • Implication (pqp \Rightarrow q): This is false only when pp is true and qq is false. Otherwise, it is true.
  • Negation (p\sim p): This is true when pp is false, and false when pp is true.
  • Conjunction (pqp \wedge q): This is true only when both pp and qq are true.
  • Disjunction (pqp \vee q): This is true when either pp or qq or both are true. It is false only when both pp and qq are false.
  • Tautology: A statement that is always true, regardless of the truth values of its components.
  • Contradiction: A statement that is always false, regardless of the truth values of its components.

Step-by-Step Solution

Step 1: Analyze Statement S1: (pq)((p)q)(p \Rightarrow q) \vee((\sim p) \wedge q)

We need to determine if the given statement is a tautology. We'll construct a truth table to evaluate the statement for all possible truth values of pp and qq.

Step 2: Construct the Truth Table for S1

pqppqpq(pq)(pq)TTFFTTTFFFFFFTTTTTFFTFTT\begin{array}{|c|c|c|c|c|c|} \hline p & q & \sim p & \sim p \wedge q & p \Rightarrow q & (p \Rightarrow q) \vee (\sim p \wedge q) \\ \hline T & T & F & F & T & T \\ \hline T & F & F & F & F & F \\ \hline F & T & T & T & T & T \\ \hline F & F & T & F & T & T \\ \hline \end{array}
  • Column 1 & 2 (p & q): All possible combinations of truth values for pp and qq.
  • Column 3 (p\sim p): Negation of pp. If pp is true, p\sim p is false, and vice versa.
  • Column 4 (pq\sim p \wedge q): Conjunction of p\sim p and qq. It is true only when both p\sim p and qq are true.
  • Column 5 (pqp \Rightarrow q): Implication of pp to qq. It is false only when pp is true and qq is false.
  • Column 6 ((pq)(pq)(p \Rightarrow q) \vee (\sim p \wedge q)): Disjunction of (pq)(p \Rightarrow q) and (pq)(\sim p \wedge q). It is true if either (pq)(p \Rightarrow q) or (pq)(\sim p \wedge q) or both are true.

Step 3: Determine if S1 is a Tautology

From the last column of the truth table, we see that the statement (pq)(pq)(p \Rightarrow q) \vee (\sim p \wedge q) is not always true. It is false when pp is true and qq is false. Therefore, S1 is not a tautology.

Step 4: Analyze Statement S2: (qp)((p)q)(q \Rightarrow p) \Rightarrow((\sim p) \wedge q)

We need to determine if the given statement is a contradiction. We'll construct a truth table to evaluate the statement for all possible truth values of pp and qq.

Step 5: Construct the Truth Table for S2

pqpqp(p)q(qp)((p)q)TTFTFFTFFTFFFTTFTTFFTTFF\begin{array}{|c|c|c|c|c|c|} \hline p & q & \sim p & q \Rightarrow p & (\sim p) \wedge q & (q \Rightarrow p) \Rightarrow ((\sim p) \wedge q) \\ \hline T & T & F & T & F & F \\ \hline T & F & F & T & F & F \\ \hline F & T & T & F & T & T \\ \hline F & F & T & T & F & F \\ \hline \end{array}
  • Column 1 & 2 (p & q): All possible combinations of truth values for pp and qq.
  • Column 3 (p\sim p): Negation of pp. If pp is true, p\sim p is false, and vice versa.
  • Column 4 (qpq \Rightarrow p): Implication of qq to pp. It is false only when qq is true and pp is false.
  • Column 5 ((p)q)((\sim p) \wedge q): Conjunction of p\sim p and qq. It is true only when both p\sim p and qq are true.
  • Column 6 ((qp)((p)q))((q \Rightarrow p) \Rightarrow ((\sim p) \wedge q)): Implication of (qp)(q \Rightarrow p) to ((p)q)((\sim p) \wedge q). It is false only when (qp)(q \Rightarrow p) is true and ((p)q)((\sim p) \wedge q) is false.

Step 6: Determine if S2 is a Contradiction

From the last column of the truth table, we see that the statement (qp)((p)q)(q \Rightarrow p) \Rightarrow ((\sim p) \wedge q) is not always false. It is true when pp is false and qq is true. Therefore, S2 is not a contradiction.

Common Mistakes & Tips

  • Be careful with the truth table for implication. pqp \Rightarrow q is only false when pp is true and qq is false.
  • Remember the definitions of tautology and contradiction.
  • It is very helpful to create a truth table for each statement separately.

Summary

We analyzed the two statements S1 and S2 using truth tables. We found that S1 is not a tautology because it is false when pp is true and qq is false. We also found that S2 is not a contradiction because it is true when pp is false and qq is true. Therefore, neither S1 nor S2 is true.

Final Answer

The final answer is \boxed{neither (S1) and (S2) is True}, which corresponds to option (A).

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