Which one of the following statements is not a tautology?

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JEE Mains Previous Paper 1 (Held On: 08 Apr 2019 Shift 2)
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  1. (p ∨ q) → (p ∨ (~q))
  2. (p ∧ q) → (~p) ∨ q
  3. p → (p ∨ q)
  4. (p ∧ q) → p

Answer (Detailed Solution Below)

Option 1 : (p ∨ q) → (p ∨ (~q))
Free
JEE Main 04 April 2024 Shift 1
13.1 K Users
90 Questions 300 Marks 180 Mins

Detailed Solution

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 Explanation:

p

q

~q

p ~q

~p

p ~q

T

T

F

T

F

F

T

F

T

T

F

T

F

T

F

F

T

F

F

F

T

T

T

F

 

p

q

p q

p → p q

p q

p q p

T

T

T

T

T

T

T

F

T

T

F

T

F

T

T

T

F

T

F

F

F

T

F

T

 

p

q

~p q

(p q) (~p) q

(p q) (p (~q))

T

T

T

T

T

T

F

F

T

T

F

T

T

T

F

F

F

T

T

T

 

A tautology is a formula or assertion that is true in every possible interpretation. So, by the truth table (p ∨ q) → (p ∨ (~q)) statement is not a tautology.

A tautology is a statement that is always true, no matter what. If you construct a truth table for a statement and all of the column values for the statement are true (T), then the statement is a tautology because it's always true!
 

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