Answer:
See steps below
Step-by-step explanation:
a)
<em>equivalence of (r implies s) with (not r or s)</em>
<em>De Morgan's Law</em>
<em>Double negation</em>
<em>Distributive Law</em>
The last expression is in CNF.
b)
i)
Modus Ponens states the following,
If (p implies q) is true and p is true, then q is true.
By watching the truth table of implication
We can notice that the only row that satisfies
(p implies q) is true and p is true
is the first row, so q must be true.
ii)
Modus Tollens states that if (p implies q) is true and (not q) is true, then (not p) is true.
By watching the following truth table
We can notice that the only row that satisfies (p implies q) is true and (not q) is true, is the fourth row, so (not p) must be true.