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JEE Main 2019
Mathematical Reasoning
Mathematical Reasoning
Easy

Question

The Boolean expression (pq)(qp)(p \wedge \sim q) \Rightarrow (q \vee \sim p) is equivalent to :

Options

Solution

Key Concepts and Formulas

  • Implication: ABA \Rightarrow B is equivalent to AB\sim A \vee B.
  • Truth Table for AND: pqp \wedge q is true only when both pp and qq are true.
  • Truth Table for OR: pqp \vee q is true when at least one of pp or qq is true.
  • Truth Table for NOT: p\sim p is the negation of pp.

Step-by-Step Solution

Step 1: Construct the truth table for the given expression (pq)(qp)(p \wedge \sim q) \Rightarrow (q \vee \sim p).

We will evaluate the expression for all possible truth values of pp and qq. This is a standard method for simplifying Boolean expressions.

ppqqp\sim pq\sim qpqp \wedge \sim qqpq \vee \sim p(pq)(qp)(p \wedge \sim q) \Rightarrow (q \vee \sim p)
TTFFFTT
TFFTTFF
FTTFFTT
FFTTFTT

Step 2: Construct the truth table for the option (A) qpq \Rightarrow p.

Using the implication rule ABABA \Rightarrow B \equiv \sim A \vee B, we have qpqpq \Rightarrow p \equiv \sim q \vee p.

ppqqq\sim qqpq \Rightarrow p (qp\equiv \sim q \vee p)
TTFT
TFTT
FTFF
FFTT

Step 3: Construct the truth table for the option (B) pqp \Rightarrow q.

Using the implication rule ABABA \Rightarrow B \equiv \sim A \vee B, we have pqpqp \Rightarrow q \equiv \sim p \vee q.

ppqqp\sim ppqp \Rightarrow q (pq\equiv \sim p \vee q)
TTFT
TFFF
FTTT
FFTT

Step 4: Construct the truth table for the option (C) qp\sim q \Rightarrow p.

Using the implication rule ABABA \Rightarrow B \equiv \sim A \vee B, we have qp(q)pqp\sim q \Rightarrow p \equiv \sim (\sim q) \vee p \equiv q \vee p.

ppqqq\sim qqp\sim q \Rightarrow p (qp\equiv q \vee p)
TTFT
TFTT
FTFT
FFTF

Step 5: Construct the truth table for the option (D) pqp \Rightarrow \sim q.

Using the implication rule ABABA \Rightarrow B \equiv \sim A \vee B, we have pqpqp \Rightarrow \sim q \equiv \sim p \vee \sim q.

ppqqp\sim pq\sim qpqp \Rightarrow \sim q (pq\equiv \sim p \vee \sim q)
TTFFF
TFFTT
FTTFT
FFTTT

Step 6: Compare the truth tables.

From Step 1, the truth table for (pq)(qp)(p \wedge \sim q) \Rightarrow (q \vee \sim p) is T, F, T, T.

From Step 2, the truth table for qpq \Rightarrow p is T, T, F, T.

From Step 3, the truth table for pqp \Rightarrow q is T, F, T, T.

From Step 4, the truth table for qp\sim q \Rightarrow p is T, T, T, F.

From Step 5, the truth table for pqp \Rightarrow \sim q is F, T, T, T.

Comparing the truth tables, we see that (pq)(qp)(p \wedge \sim q) \Rightarrow (q \vee \sim p) is equivalent to pqp \Rightarrow q.

Common Mistakes & Tips

  • Remember that ABA \Rightarrow B is equivalent to AB\sim A \vee B. This is crucial for simplifying implications.
  • Be careful with the order of operations and negations when constructing the truth tables.
  • Double check the truth values in your truth tables to avoid errors.

Summary

We constructed truth tables for the given expression and all the options. By comparing the truth tables, we found that the expression (pq)(qp)(p \wedge \sim q) \Rightarrow (q \vee \sim p) is equivalent to pqp \Rightarrow q.

Final Answer

The final answer is \boxed{p \Rightarrow q}, which corresponds to option (B).

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