Skip to main content
Back to Mathematical Reasoning
JEE Main 2021
Mathematical Reasoning
Mathematical Reasoning
Medium

Question

The statement [p((pq))]\sim[p \vee(\sim(p \wedge q))] is equivalent to :

Options

Solution

Key Concepts and Formulas

  • De Morgan's Laws:
    • (pq)(p)(q)\sim(p \vee q) \equiv (\sim p) \wedge (\sim q)
    • (pq)(p)(q)\sim(p \wedge q) \equiv (\sim p) \vee (\sim q)
  • Distributive Laws:
    • p(qr)(pq)(pr)p \wedge (q \vee r) \equiv (p \wedge q) \vee (p \wedge r)
    • p(qr)(pq)(pr)p \vee (q \wedge r) \equiv (p \vee q) \wedge (p \vee r)
  • Negation of Negation: (p)p\sim(\sim p) \equiv p
  • Commutative Laws:
    • pqqpp \vee q \equiv q \vee p
    • pqqpp \wedge q \equiv q \wedge p
  • Associative Laws:
    • (pq)rp(qr)(p \vee q) \vee r \equiv p \vee (q \vee r)
    • (pq)rp(qr)(p \wedge q) \wedge r \equiv p \wedge (q \wedge r)
  • Identity Laws:
    • pFpp \vee F \equiv p
    • pTpp \wedge T \equiv p
  • Inverse Laws:
    • p(p)Tp \vee (\sim p) \equiv T
    • p(p)Fp \wedge (\sim p) \equiv F
  • Absorption Laws:
    • p(pq)pp \vee (p \wedge q) \equiv p
    • p(pq)pp \wedge (p \vee q) \equiv p
  • Conditional and Biconditional Statements: These are not strictly necessary for this question, but are good to know.

Step-by-Step Solution

Step 1: Apply De Morgan's Law to the outermost negation. We have the statement [p((pq))]\sim[p \vee (\sim(p \wedge q))]. Applying De Morgan's Law, we distribute the negation and change the \vee to \wedge: [p((pq))](p)((pq))\sim[p \vee (\sim(p \wedge q))] \equiv (\sim p) \wedge \sim(\sim(p \wedge q))

Step 2: Simplify the double negation. We have ((pq))\sim(\sim(p \wedge q)), which simplifies to (pq)(p \wedge q). (p)((pq))(p)(pq)(\sim p) \wedge \sim(\sim(p \wedge q)) \equiv (\sim p) \wedge (p \wedge q)

Step 3: Apply the associative law of conjunction. We can regroup the terms using the associative law: (p)(pq)(pp)q(\sim p) \wedge (p \wedge q) \equiv (\sim p \wedge p) \wedge q

Step 4: Apply the inverse law. We know that p(p)Fp \wedge (\sim p) \equiv F. (pp)qFq(\sim p \wedge p) \wedge q \equiv F \wedge q

Step 5: Apply the identity law. We know that FqFF \wedge q \equiv F. FqFF \wedge q \equiv F

Step 6: Analyze the options to find an equivalent expression. We need to find an option that is always false. Option (A): ((pq))q(\sim(p \wedge q)) \wedge q ((pq))q((p)(q))q((p)q)((q)q)((p)q)F(p)q(\sim(p \wedge q)) \wedge q \equiv ((\sim p) \vee (\sim q)) \wedge q \equiv ((\sim p) \wedge q) \vee ((\sim q) \wedge q) \equiv ((\sim p) \wedge q) \vee F \equiv (\sim p) \wedge q This is not always false.

Option (B): (pq)(p)(q)\sim(p \vee q) \equiv (\sim p) \wedge (\sim q). This is not always false.

Option (C): (pq)(p)(p(p))qFqF(p \wedge q) \wedge (\sim p) \equiv (p \wedge (\sim p)) \wedge q \equiv F \wedge q \equiv F. This is always false.

Option (D): (pq)(p)(q)\sim(p \wedge q) \equiv (\sim p) \vee (\sim q). This is not always false.

Since our simplified expression is FF, option (C) is equivalent.

However, the correct answer is stated to be option (A). Let's re-examine the initial problem and the target.

We simplified the original expression to (p)(pq)(\sim p) \wedge (p \wedge q). We want to show this is equivalent to ((pq))q(\sim(p \wedge q)) \wedge q.

((pq))q((p)(q))q((p)q)((q)q)((p)q)F(p)q(\sim(p \wedge q)) \wedge q \equiv ((\sim p) \vee (\sim q)) \wedge q \equiv ((\sim p) \wedge q) \vee ((\sim q) \wedge q) \equiv ((\sim p) \wedge q) \vee F \equiv (\sim p) \wedge q.

Now, let's see if (p)(pq)(p)q(\sim p) \wedge (p \wedge q) \equiv (\sim p) \wedge q.

(p)(pq)((p)p)qFqF(\sim p) \wedge (p \wedge q) \equiv ((\sim p) \wedge p) \wedge q \equiv F \wedge q \equiv F. (p)q(\sim p) \wedge q is not always F.

Let's analyze option (A) again: ((pq))q(\sim(p \wedge q)) \wedge q. ((pq))q((p)(q))q((p)q)((q)q)((p)q)F(p)q(\sim(p \wedge q)) \wedge q \equiv ((\sim p) \vee (\sim q)) \wedge q \equiv ((\sim p) \wedge q) \vee ((\sim q) \wedge q) \equiv ((\sim p) \wedge q) \vee F \equiv (\sim p) \wedge q.

The original expression simplifies to FF. We need to show ((pq))q(\sim(p \wedge q)) \wedge q is also FF. ((pq))q(pq)q(pq)(qq)(pq)Fpq(\sim(p \wedge q)) \wedge q \equiv (\sim p \vee \sim q) \wedge q \equiv (\sim p \wedge q) \vee (\sim q \wedge q) \equiv (\sim p \wedge q) \vee F \equiv \sim p \wedge q. This is equal to T when p is F and q is T. So, option A is NOT correct.

There seems to be an error in the given answer. The original expression reduces to FF, which is equivalent to option (C).

Common Mistakes & Tips

  • Be careful when applying De Morgan's Laws. Remember to negate each term and change the connective.
  • Always double-check your simplifications to avoid errors.
  • When using truth tables, ensure you consider all possible combinations of truth values for the variables.

Summary

We started with the given expression [p((pq))]\sim[p \vee(\sim(p \wedge q))] and simplified it using De Morgan's Laws, the associative law, and inverse law to obtain FF. Comparing this result with the options, we found that option (C), (pq)(p)(p \wedge q) \wedge(\sim p), also simplifies to FF. Therefore, the given answer of option (A) is incorrect, and the correct answer should be option (C).

Final Answer

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

Practice More Mathematical Reasoning Questions

View All Questions