# UGCNET-Nov2017-ii-8

1 vote
905 views

Let $P$ and $Q$ be two propositions $\neg (P \leftrightarrow Q)$ is equivalent to

1. $P\leftrightarrow \neg Q$
2. $\neg P\leftrightarrow Q$
3. $\neg P \leftrightarrow \neg Q$
4. $Q\rightarrow P$

recategorized
0
Options 1 and 2 both are correct.
0
yes both are correct
0
Option 1) and 2) both are correct .

Right?
0
Yes, both 1st and 2nd are correct.
0
Why not option 1) ?
1

P↔Q =  P Exnor Q

So ~ ( P Exnor Q) = ~  P Exnor Q =  P Exnor ~Q = P Exor Q

Yes both are true.

P Q $\sim p$ $\sim Q$ $Q \rightarrow P$ $\sim(P \leftrightarrow Q)$ $P \leftrightarrow \sim Q$
$\sim P \leftrightarrow Q$
$\sim P \leftrightarrow \sim Q$
0 0 1 1 1 0 0 0 1
0 1 1 0 0 1 1 1 0
1 0 0 1 1 1 1 1 0
1 1 0 0 1 0 0 0 1

Both option(1)and (2) is the correct choice.

selected
The answer will be both 1)P↔∼Q & 2)∼P↔Q

....

Option 1 is correct

Option 2 is also correct

$\sim$(P $\rightarrow$ Q)

= $\sim$( (P $\rightarrow$ Q) ^ (Q $\rightarrow$ P) )

= $\sim$ ( ($\sim$P v Q) ^ ( $\sim$Q v P) )

= $\sim$($\sim$P v Q) v $\sim$($\sim$Q v P)

= (P ^ $\sim$Q) v (Q v $\sim$P) = P$\bigoplus$Q

Using distributive law. (a + bc) = (a + b).(b + c)

= ( (P ^ $\sim$Q) v Q) ^ ( (P ^ $\sim$Q) v $\sim$P)

= ( ( P v Q)^($\sim$Q v Q)) ^ ( ( $\sim$P v  P) ^ ($\sim$Q v $\sim$P) )

= ( ( P v Q) ^ ( $\sim$Q v $\sim$ P)

Now here we have two choices.

1. ($\sim$P $\rightarrow$ Q) ^ ( Q $\rightarrow$ $\sim$P) = $\sim$P $\leftrightarrow$ Q

2. ($\sim$Q $\rightarrow$ P) ^ (P $\rightarrow$ $\sim$ Q) = P $\leftrightarrow$ $\sim$Q.

So both 1 and 2 option is correct.

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