you want to test for equivalency of the 2 statements.
the statements are:
(not p) or (not q)
not (p and q)
if the statements are equivalent, then they will have the same truth table.
we'll construct a table and see what happens.
here's a reference you can look at later if you're interested.
http://www.bookrags.com/research/demorgans-laws-wom/
our truth table looks like this:
p q ~p ~q (p ^ q) (~p v ~q) (~(p ^ q)) (~p v ~q) <-> (~(p ^ q))
T T F F T F F T
T F F T F T T T
F T T F F T T T
F F T T F T T T
you start with the basic variables and create your truth table from that.
first column is p (truth table for p)
second column is q (truth table for q)
third column is ~p (truth table for not p - this is the negation of p)
fourth column is ~q (truth table for not q - this is the negation of q)
fifth column is (p ^ q) truth table for (p and q)
sixth column is (~p v ~q) truth table for (not p or not q)
seventh column is (~(p v q) truth table for (not (p and q) - this is the negation of (p and q)
eighth column is (~p v ~q) <-> (~(p ^ q))
this is the equivalency statement for (not p or not q) and (not (p and q)).
as seen from this table:
if p is true, then not p is false.
if p is false, then not p is true.
if q is true, then not q is false.
if q is false, then not q is true.
(p ^ q) is true only if p and q are both true. If they are mixed or both false, then (p ^ q) is false.
~(p^q) is the negation of (p ^ q).
if (p ^ q) is true, then ~(p ^ q) is false.
if (p ^ q) is false, then ~(p ^ q) is true.
(~p v ~q) is true if ~p or ~q is true.
only 1 of them is required to be true.
(~p v ~q) is false only if ~p and ~q are both false. If they are mixed or both true, then (~p v ~q) is true.
(~p or ~q) <-> (~(p ^ q)) is the equivalency statement.
it has the form of A if and only if B.
in this statement, A is equal to (~p or ~q) and B is equal to (~(p ^ q)).
since (~p or ~q) <-> (~(p ^ q)) is true under all conditions, then the 2 statements are equivalent.