# Homework Help: Demorgan's law

1. Feb 1, 2010

### magnifik

1. The problem statement, all variables and given/known data
(A'B')'=A'+B' is a representation of DeMorgan's Law. True or false?

3. The attempt at a solution
Is this saying that not A and not B is equal to A nor B?? i'm confused because each individual letter has its own notation rather than AB together. idk if that made sense...

2. Feb 1, 2010

### Staff: Mentor

This is saying - not(not(A) AND not(B)) = not(A) OR not(B).

I don't understand what you're saying here "each individual letter has its own notation rather than AB together." There is no AB "together" as its own symbol. AB means A AND B.

3. Feb 1, 2010

### magnifik

ohhh. ok. that makes more sense. but is it possible for not(not(A) AND not(B)) to become an OR problem?

4. Feb 1, 2010

### Staff: Mentor

I don't know - maybe. That's what your problem is all about. There are two forms of DeMorgan's Law:

~(A AND B) = ~A OR ~B
~(A OR B) = ~A AND ~B
The tilde - ~ - is commonly used for negation (i.e., "not").

In your problem, work with one of the sides and see if you can make it look like the other.

5. Feb 1, 2010

### magnifik

my thoughts are that this would be false because it would have to be
~(~A and ~B) = ~(~A or ~B)

6. Feb 1, 2010

### Staff: Mentor

No, ~(~A and ~B) = ~(~A) or ~(~B), right?

What is ~(~A)?