# Constructing truth tables?

• Apr 6th 2011, 06:58 AM
Cockchestner007
Constructing truth tables?
how would you construct a truth table for these compound proposition? im so confused (Crying)

(a) if P then ((notP) and Q)

(b) P and ((not P) and Q)

(c) (not P) or (not Q)
• Apr 6th 2011, 07:09 AM
Ackbeet
All of those have two variables in them, which means you need $2^{2}$ rows in the table. In general, if you have $n$ variables, you need $2^{n}$ rows. I'll start you off on the first one. I tend to build up truth tables from smaller chunks of the expression:

$
\begin{array}{c|c|c|c}
P &Q &\neg P &(\neg P)\land Q\\ \hline
T &T &F &F\\
T &F &F &F\\
F &T &T &T\\
F &F &T &F
\end{array}
$

Do you see how to continue?
• Apr 6th 2011, 07:51 AM
Cockchestner007
Thanks so much, but what I don't understand is when it says "not" "and" "or" what does it mean?
• Apr 6th 2011, 07:56 AM
Plato
Quote:

Originally Posted by Cockchestner007
Thanks so much, but what I don't understand is when it says "not" "and" "or" what does it mean?

Go to this web site and play around with various examples.
Change to just 'p and q'. Then to 'p or q' etc.