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JEE Main 2019
Mathematical Reasoning
Mathematical Reasoning
Easy

Question

If p \Rightarrow (q \vee r) is false, then the truth values of p, q, r are respectively :-

Options

Solution

Key Concepts and Formulas

  • Implication: The statement pqp \Rightarrow q (p implies q) is false only when p is true and q is false.
  • Disjunction: The statement qrq \vee r (q or r) is true if either q is true, r is true, or both are true. It is false only when both q and r are false.
  • Negation: The negation of a statement p, denoted by p\sim p, has the opposite truth value of p. If p is true, p\sim p is false, and vice versa.

Step-by-Step Solution

Step 1: Understand the given condition. We are given that p(qr)p \Rightarrow (q \vee r) is false. We need to determine the truth values of p, q, and r.

Step 2: Apply the definition of implication. The implication p(qr)p \Rightarrow (q \vee r) is false if and only if pp is true and (qr)(q \vee r) is false. Therefore, we have: p=Truep = \text{True} qr=Falseq \vee r = \text{False}

Step 3: Determine the truth values of q and r. Since qrq \vee r is false, it means that both q and r must be false. The disjunction (OR) is only false when both statements are false. Therefore: q=Falseq = \text{False} r=Falser = \text{False}

Step 4: Summarize the truth values. We found that pp is true, qq is false, and rr is false.

Common Mistakes & Tips

  • Remember the truth table for implication. It's crucial to know when pqp \Rightarrow q is false.
  • Understand the difference between conjunction (AND) and disjunction (OR). qrq \wedge r is only true if both q and r are true, while qrq \vee r is false only if both q and r are false.
  • When dealing with false implications, always start by making the left side true and the right side false.

Summary

We are given that p(qr)p \Rightarrow (q \vee r) is false. This occurs only when p is true and (qr)(q \vee r) is false. For (qr)(q \vee r) to be false, both q and r must be false. Therefore, the truth values of p, q, and r are true, false, and false, respectively.

Final Answer The final answer is \boxed{T, F, F}, which corresponds to option (B).

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