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JEE Main 2019
Mathematical Reasoning
Mathematical Reasoning
Easy

Question

If the truth value of the statement p \to (~q \vee r) is false (F), then the truth values of the statements p, q, r are respectively :

Options

Solution

Key Concepts and Formulas

  • The implication pqp \to q is false only when pp is true and qq is false. Otherwise, it is true.
  • The negation of a statement changes its truth value: if pp is true, then p\sim p is false, and vice versa.
  • The disjunction pqp \vee q is true if at least one of pp or qq is true. It is false only when both pp and qq are false.

Step-by-Step Solution

Step 1: Understand the given information.

We are given that the truth value of p(qr)p \to (\sim q \vee r) is false (F). This is our starting point. We need to find the truth values of pp, qq, and rr that make this statement false.

Step 2: Apply the condition for the falsity of an implication.

For the implication p(qr)p \to (\sim q \vee r) to be false, we must have pp being true (T) and (qr)(\sim q \vee r) being false (F). This is because pqp \to q is only false if pp is true and qq is false.

So, we have p=Tp = T and qr=F\sim q \vee r = F.

Step 3: Analyze the disjunction.

For qr\sim q \vee r to be false, both q\sim q and rr must be false. This is because the disjunction aba \vee b is only false if both aa and bb are false.

So, we have q=F\sim q = F and r=Fr = F.

Step 4: Determine the truth value of qq.

Since q=F\sim q = F, it means that qq must be true. This is because the negation of a false statement is true.

So, q=Tq = T.

Step 5: Summarize the truth values.

We have found that p=Tp = T, q=Tq = T, and r=Fr = F.

Common Mistakes & Tips

  • Remember the truth table for implication (pqp \to q). It's only false when pp is true and qq is false.
  • Be careful with negations. If q\sim q is false, then qq is true, and vice versa.
  • When dealing with disjunctions (pqp \vee q), remember that it's only false when both pp and qq are false.

Summary

We are given that the statement p(qr)p \to (\sim q \vee r) is false. Using the truth table for implication, we deduce that pp must be true and (qr)(\sim q \vee r) must be false. For the disjunction (qr)(\sim q \vee r) to be false, both q\sim q and rr must be false. From q=F\sim q = F, we get q=Tq = T. Therefore, the truth values of pp, qq, and rr are T, T, and F, respectively.

Final Answer

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

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