# Could use some help please! (boolean algebra)

Discussion in 'Homework Help' started by tomro99, Oct 9, 2013.

1. ### tomro99 Thread Starter New Member

Oct 9, 2013
4
0
I have a couple questions on my homework that I have been stumped on for the longest time. If someone could help me out, it would be greatly appreciated. BTW, the subject is boolean algebra

Question 1:
Give a logical expression with variables p,q, and r that is true if p and q are false and r is true.

Question 2:
Find a logical expression whose truth table is the table below:
p q r ????
T T T F
T T F F
T F T T
T F F T
F T T F
F T F F
F F T T
F F F F

Any help would be greatly appreciated. Thanks so much in advance.

2. ### WBahn Moderator

Mar 31, 2012
18,089
4,917
First, show YOUR best attempt to solve YOUR homework. That will give us a starting point to help guide you from where you are to where you need to be.

3. ### MrChips Moderator

Oct 2, 2009
12,648
3,458
Why did you not say that in your title?

4. ### tomro99 Thread Starter New Member

Oct 9, 2013
4
0
my apologies. I will go ahead and post what I have so far

5. ### tomro99 Thread Starter New Member

Oct 9, 2013
4
0
I should have. This is my first thread but now I know to post the subject in the title. Thanks for pointing that out

6. ### tomro99 Thread Starter New Member

Oct 9, 2013
4
0
at the moment, for question #1, I have this truth table

p q r
T T T
T T F
T F T
T F F
F T T
F T F
F F T <-------- So I need a logical expression for this row here.
F F F

Thats where I am stuck at the moment.

As for the second question, I cam up with: ~r∧(p→~q)
But that only gives me the first two rows. Once it gets to the 3rd (need a T), I get another false.

7. ### WBahn Moderator

Mar 31, 2012
18,089
4,917
Okay, that gives us the starting point.

First thing is that you are using a notation that most people here are not going to be familiar with or at least not real comfortable with. So let's be sure we are on the same page.

~r∧(p→~q)

The ~ operator is logical negation, correct?

The ∧ operator is the logical conjunction (logical AND), correct?

The → operator is the logical disjunction (logical OR), correct?

This last one, in particular, is the one I'm not sure of what you mean because I've seen it used for logical implication, which is seldom used in engineering Boolean algebra.

The operators you will find most of us here are most comfortable with are

NOT: A'
AND: A*B or AB
OR: A+B

One place that you might find useful is the following blog entry: