I have done a truth table below and i need someone to check it for me. I am not sure if I have it set up right. The ~q and --> has me a little confussed..
The truth table contains only 4 lines, not 8.
So first you need to learn the formula for the number of lines
in a truth table. That formula is
When there is one letter as in p-->(~p^p), there are
only 21 or 2 lines in the truth table.
When there are 2 letters as in ~pV(~q^p), there are 2² or 4
lines in the truth table.
When there are 3 letters as in pV(q^r), there are 2³ or
8 lines in the truth table.
Your statement
~q-->(p^q)
has only 2 letters, p and q, so you should only have
2² or 4 lines:
We break ~q-->(p^q) down into its five parts
(1) p
(2) q
(3) ~q
(4) (p^q)
(5) ~q-->(p^q)
The first parts (1) and (2) are the letters.
Then we can get the truth value for (3) ~q by looking
at (2) the truth value for q
Then (4) we can get the truth value for p^q by looking
at (1) and (2), the truth values for p and q
Finally we can get the truth value for the whole
expression by looking at (3) and (4), the truth values
for ~q and (p^q).
So we make five columns on the truth tables.
(you can leave out the line numbers if you like)
line# p q -q (p^q) ~q-->(p^q)
_________________________________
1
2
3
4
We start out putting TTFF under p and TFTF
under q:
line# p q -q (p^q) ~q-->(p^q)
_________________________________
1 T T
2 T F
3 F T
4 F F
Since the list under q is TFTF we just put the
opposite, FTFT, under ~q:
line# p q -q (p^q) ~q-->(p^q)
_________________________________
1 T T F
2 T F T
3 F T F
4 F F T
Under the (p^q) we put T on the line that has p and q
both as T and we put F otherwise. The only line that gets
a T is line# 1 because that's the only line in
which p and q both have T's. So under the (p^q) we put TFFF
line# p q -q (p^q) ~q-->(p^q)
_________________________________
1 T T F T
2 T F T F
3 F T F F
4 F F T F
Finally under the conditional --> we put F only on lines
when there is a T under whats on the left of -->, which is
~q and an F under what's on the right of the -->, which is
(p^q) . That is the case in lines #2 and #4, so under the
--> we put TFTF in the last column:
line# p q -q (p^q) ~q-->(p^q)
_________________________________
1 T T F T T
2 T F T F F
3 F T F F T
4 F F T F F
That's it. The truth table is TFTF which happens
to be the same as what's under q, so the expression
~q-->(p^q) is equivalent to q. Later on, you'll show that
this way:
~q-->(p^q) given
~(~q) v (p^q) definition of conditional
q v (p^q) negation of a negation
(T^q) v (p^q) tautology (T) is the indentity for conjunction
(Tvp)^q factoring out ^q on the right
T^q tautology (T) is the annihilator for disjunction
q tautology is the identity for conjunction
Edwin