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JEE Main 20231 FebruaryEvening Shift
Exam
JEE Main
Year
2023
Date
1 February
Shift
Evening Shift
Subject
Mathematics
Chapter
Mathematical Reasoning

JEE Main 2023 · 1 February · Evening Shift · Mathematics · Mathematical Reasoning

Which of the following statements is a tautology?

Which of the following statements is a tautology?

Options

  1. Ap→(p∧(p→q))p \to \left(p ∧ \left(p \to q\right)\right)
  2. B(p∧q)→( (p)→q)\left(p ∧ q\right) \to \left(~ \left(p\right) \to q\right)
  3. C(p∧(p→q))→ q\left(p ∧ \left(p \to q\right)\right) \to ~ q
  4. Dp∨(p∧q)p ∨ \left(p ∧ q\right)

Correct answer

B. (p∧q)→( (p)→q)\left(p ∧ q\right) \to \left(~ \left(p\right) \to q\right)

Step-by-step solution

We know,

A \to B ≡ ~ A ∨ B</p><p>Nowsolvingalloptionsonebyoneweget,</p><p>Now solving all options one by one we get,

\left(A\right)p \to \left(p ∧ \left(p \to q\right)\right)</p><p></p><p>≡ \left(~ p\right) ∨ \left(p ∧ \left(~ p ∨ q\right)\right)

≡( p)∨(f∨(p∧q))≡ \left(~ p\right) ∨ \left(f ∨ \left(p ∧ q\right)\right)

≡ p∨(p∧q)≡( p∨p)∧( p∨q)</p><p>≡ ~ p ∨ \left(p ∧ q\right) ≡ \left(~ p ∨ p\right) ∧ \left(~ p ∨ q\right)</p><p>≡ ~ p ∨ q</p><p>Whichisnotatautology</p><p>Which is not a tautology

\left(B\right)\left(p ∧ q\right) \to \left(~ p \to q\right)

≡ (p∧q)≡ ~ \left(p ∧ q\right) ∨ \left(p ∨ q\right)</p><p></p><p>≡ ~ p ∨ ~ q ∨ \left(p ∨ q\right)

≡ p∨p∨ q∨q≡ ~ p ∨ p ∨ ~ q ∨ q

≡T∨T≡T≡ T ∨ T ≡ T

Tautology</p><p>\left(C\right) \left(p ∧ \left(p \to q\right)\right) \to ~ q</p><p></p><p>≡ ~ \left(p ∧ \left(~ p ∨ q\right)\right) ∨ ~ q

≡ (p∧q)≡ ~ \left(p ∧ q\right) ∨ ~ q</p><p></p><p>≡ ~ p ∨ ~ q</p><p>Whichisnotatautology</p><p>Which is not a tautology

\left(D\right)p∨(p∧q)p ∨ \left(p ∧ q\right) ≡ p</p><p>Whichisnotatautology</p><p>Which is not a tautology

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