in Mathematical Logic
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in Mathematical Logic
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1 is not valid while 2 is valid .What is the answer?

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Correct.

Can you please provide the steps you used while solving this questions.
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$1.\left \{ \exists x A(x),\forall x \,\,\, \text{           }^{'} \left \{ A(x) \wedge Q(x) \right \} \Rightarrow \exists x Q(x)\right \}$

 

can be wriiten as

$1.\left \{ \exists x A(x) \wedge  \text{         }^{'} \, \exists x \left \{ A(x) \wedge Q(x) \right \}  \Rightarrow \exists x Q(x)\right \}$

To check the validity of the logic ,we need to prove 

True $\Rightarrow$True

for LHS to be true,

$\exists x A(x)$ must be true 

AND

$\left \{ A(x) \wedge Q(x) \right \}$ must be false so that ¬false=true 

and then true AND true=TRUE

As $\left \{ A(x) \wedge Q(x) \right \}$ must be false and we know already $\exists x A(x)$ must be true 

so $\exists x Q(x)$ must be false but RHS says $\exists x Q(x)$ is true hence true $\Rightarrow$ false .hence whole logic is invalid

 

so same for part 2

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