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JEE Main 202225 JulyMorning Shift
Exam
JEE Main
Year
2022
Date
25 July
Shift
Morning Shift
Subject
Mathematics
Chapter
Mathematical Reasoning

JEE Main 2022 · 25 July · Morning Shift · Mathematics · Mathematical Reasoning

Which of the following statements is a tautology?

Which of the following statements is a tautology?

Options

  1. A(( p)∨q)⇒p\left(\left(~ p\right) ∨ q\right) ⇒ p
  2. Bp⇒(( p)∨q)p ⇒ \left(\left(~ p\right) ∨ q\right)
  3. C(( p)∨q)⇒q\left(\left(~ p\right) ∨ q\right) ⇒ q
  4. Dq⇒(( p)∨q)q ⇒ \left(\left(~ p\right) ∨ q\right)

Correct answer

D. q⇒(( p)∨q)q ⇒ \left(\left(~ p\right) ∨ q\right)

Step-by-step solution

Plotting the truth table of the following option we have,

pp qq  p~ p  q~ q  p∨q~ p ∨ q
TT TT FF FF TT
TT FF FF TT FF
FF TT TT FF TT
FF FF TT TT TT

We know that, A⇒BA ⇒ B is only false when AA is true and BB is false, now using this rule and above table we will make truth table of options,

(( p)∨q)⇒p\left(\left(~ p\right) ∨ q\right) ⇒ p p⇒(( p)∨q)p ⇒ \left(\left(~ p\right) ∨ q\right) \left(\left(~ p\right) ∨ q\right) ⇒ q</td><td></td> <td>q ⇒ \left(\left(~ p\right) ∨ q\right)</td></tr><tr><td></td> </tr> <tr> <td>T</td><td></td> <td>T</td><td></td> <td>T</td><td></td> <td>T</td></tr><tr><td></td> </tr> <tr> <td>T</td><td></td> <td>F</td><td></td> <td>T</td><td></td> <td>T</td></tr><tr><td></td> </tr> <tr> <td>F</td><td></td> <td>T</td><td></td> <td>T</td><td></td> <td>T</td></tr><tr><td></td> </tr> <tr> <td>F</td><td></td> <td>T</td><td></td> <td>F</td><td></td> <td>T</td></tr></tbody></table><p></p><p>Hence</td> </tr> </tbody></table><p> </p><p>Henceq ⇒ \left(\left(~ p\right) ∨ q\right) is tautology.

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