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JEE Main 2019
Mathematical Reasoning
Mathematical Reasoning
Easy

Question

Consider the following two propositions: P1:(pq)P1: \sim (p \to \sim q) P2:(pq)((p)q)P2:(p \wedge \sim q) \wedge (( \sim p) \vee q) If the proposition p((p)q)p \to (( \sim p) \vee q) is evaluated as FALSE, then :

Options

Solution

Key Concepts and Formulas

  • Implication: pqp \to q is FALSE only when pp is TRUE and qq is FALSE. Otherwise, it's TRUE.
  • Negation: p\sim p is TRUE if pp is FALSE, and FALSE if pp is TRUE.
  • Conjunction: pqp \wedge q is TRUE only when both pp and qq are TRUE. Otherwise, it's FALSE.
  • Disjunction: pqp \vee q is FALSE only when both pp and qq are FALSE. Otherwise, it's TRUE.

Step-by-Step Solution

Step 1: Analyze the given condition

We are given that p(pq)p \to (\sim p \vee q) is FALSE. Using the truth table for implication, this means that pp must be TRUE and (pq)(\sim p \vee q) must be FALSE. p(pq)=Fp \to (\sim p \vee q) = F This implies: p=Tand(pq)=Fp = T \quad \text{and} \quad (\sim p \vee q) = F

Step 2: Determine the truth value of p and q

Since p=Tp = T, we have p=F\sim p = F. Substituting this into (pq)=F(\sim p \vee q) = F, we get: (Fq)=F(F \vee q) = F For the disjunction to be FALSE, both terms must be FALSE. Therefore, q=Fq = F. q=Fq = F So, we have p=Tp = T and q=Fq = F.

Step 3: Evaluate proposition P1

P1:(pq)P1: \sim (p \to \sim q) Substitute p=Tp = T and q=Fq = F: P1:(TF)P1: \sim (T \to \sim F) Since F=T\sim F = T, we have: P1:(TT)P1: \sim (T \to T) Since TT=TT \to T = T, we have: P1:(T)=FP1: \sim (T) = F Thus, P1 is FALSE.

Step 4: Evaluate proposition P2

P2:(pq)((p)q)P2: (p \wedge \sim q) \wedge ((\sim p) \vee q) Substitute p=Tp = T and q=Fq = F: P2:(TF)((T)F)P2: (T \wedge \sim F) \wedge ((\sim T) \vee F) Since F=T\sim F = T and T=F\sim T = F, we have: P2:(TT)(FF)P2: (T \wedge T) \wedge (F \vee F) P2:(T)(F)P2: (T) \wedge (F) P2:FP2: F Thus, P2 is FALSE.

Step 5: Determine which option is correct

We found that P1 is FALSE and P2 is FALSE.

Common Mistakes & Tips

  • Remember that pqp \to q is only FALSE when pp is TRUE and qq is FALSE. It's TRUE in all other cases.
  • Pay close attention to the order of operations and the meaning of each logical connective (,,,\sim, \wedge, \vee, \to).
  • When evaluating compound propositions, substitute the truth values of the variables and simplify step by step.

Summary

We were given that p(pq)p \to (\sim p \vee q) is FALSE, which implied that pp is TRUE and pq\sim p \vee q is FALSE. This allowed us to deduce that p=Tp = T and q=Fq = F. Substituting these values into the expressions for P1 and P2, we found that both P1 and P2 are FALSE. Therefore, the correct option is that both P1 and P2 are FALSE.

Final Answer

The final answer is \boxed{C}, which corresponds to option (C).

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