Show that each of these conditional statements is a tautology using logical equivalences.a) (๐ โง ๐) โ ๐b) ยฌ๐ โ (๐ โ ๐)c) (๐ โง ๐) โ (๐ โ ๐)
Question
Show that each of these conditional statements is a tautology using logical equivalences.
a) (๐ โง ๐) โ ๐
b) ยฌ๐ โ (๐ โ ๐)
c) (๐ โง ๐) โ (๐ โ ๐)
Solution
Sure, let's go through each of these conditional statements one by one:
a) (๐ โง ๐) โ ๐
This statement can be rewritten using the logical equivalence of the conditional statement, which is ยฌ๐ โจ ๐. So, (๐ โง ๐) โ ๐ becomes ยฌ(๐ โง ๐) โจ ๐.
Using De Morgan's law, ยฌ(๐ โง ๐) can be rewritten as ยฌ๐ โจ ยฌ๐. So, ยฌ(๐ โง ๐) โจ ๐ becomes (ยฌ๐ โจ ยฌ๐) โจ ๐.
Using the associative law, we can rearrange this to ยฌ๐ โจ (ยฌ๐ โจ ๐).
Finally, using the law of disjunction (which states that ๐ โจ ยฌ๐ is always true), we can see that (ยฌ๐ โจ ๐) is always true, and therefore the entire statement is a tautology.
b) ยฌ๐ โ (๐ โ ๐)
This statement can be rewritten using the logical equivalence of the conditional statement, which is ยฌ๐ โจ (๐ โ ๐).
The inner conditional statement (๐ โ ๐) can also be rewritten using the logical equivalence of the conditional statement, which gives us ยฌ๐ โจ (ยฌ๐ โจ ๐).
Using the associative law, we can rearrange this to (ยฌ๐ โจ ยฌ๐) โจ ๐.
Finally, using the law of idempotency (which states that ๐ โจ ๐ is equivalent to ๐), we can simplify this to ยฌ๐ โจ ๐.
Since ยฌ๐ โจ ๐ is always true (because either ๐ is false, or ๐ is true and ๐ is true), the entire statement is a tautology.
c) (๐ โง ๐) โ (๐ โ ๐)
This statement can be rewritten using the logical equivalence of the conditional statement, which is ยฌ(๐ โง ๐) โจ (๐ โ ๐).
Using De Morgan's law, ยฌ(๐ โง ๐) can be rewritten as ยฌ๐ โจ ยฌ๐. So, ยฌ(๐ โง ๐) โจ (๐ โ ๐) becomes (ยฌ๐ โจ ยฌ๐) โจ (๐ โ ๐).
The inner conditional statement (๐ โ ๐) can also be rewritten using the logical equivalence of the conditional statement, which gives us (ยฌ๐ โจ ยฌ๐) โจ (ยฌ๐ โจ ๐).
Using the associative law, we can rearrange this to ยฌ๐ โจ (ยฌ๐ โจ (ยฌ๐ โจ ๐)).
Finally, using the law of disjunction (which states that ๐ โจ ยฌ๐ is always true), we can see that (ยฌ๐ โจ (ยฌ๐ โจ ๐)) is always true, and therefore the entire statement is a tautology.
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