Mathematical Reasoning
hard

निम्न कथनों में से कौन-सा एक, एक पुनरुक्ति (tautology) नहीं है ?

A

$\left( {p \vee q} \right) \to \left( {p \vee \left( { \sim q} \right)} \right)$

B

$\left( {p \vee q} \right) \to p$

C

$p \to \left( {p \vee q} \right)$

D

$\left( {p \wedge q} \right) \to \left( { \sim p} \right) \vee q$

(JEE MAIN-2019)

Solution

$\left( A \right)\,\,\,\,\left( {p \vee q} \right) \to \left( {p \vee \left( { \sim q} \right)} \right)$

    $ =  \sim \left( {p \vee q} \right) \vee \left( {p \vee  \sim q} \right)$

    $ = \left( { \sim p \wedge  \sim q} \right) \wedge \left( {p \vee  \sim q} \right)$

    $ \ne T$

 

$\left( B \right)\,\,\,\,\left( {p \wedge q} \right) \to p$

    $ =  \sim \left( {p \wedge q} \right) \vee p = \left( { \sim p \vee  \sim q} \right) \vee p$

    $ = \left( { \sim p \wedge p} \right) \vee  \sim q$

     $ = T$

$\left( C \right)\,\,\,\, \sim p \vee \left( {p \vee q} \right)$

      $ = \left( { \sim p \vee p} \right) \vee q = T$

$\left( D \right)\,\,\,\, \sim \left( {p \vee q} \right) \vee \left( { \sim p \vee q} \right)$

      $ = \left( { \sim p \vee  \sim q} \right) \vee \left( { \sim p \vee q} \right)$

      $ =  \sim p \vee T = T$

 

Standard 11
Mathematics

Similar Questions

Start a Free Trial Now

Confusing about what to choose? Our team will schedule a demo shortly.