Logic: Negating if then statement

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In summary, the statement (p\veeq) ---> (p \wedge q) can be negated as \negp\wedge\negq. Using de Morgan's law, it can be further simplified to (p v q) ^ (~p v ~q).
  • #1
mohabitar
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I'm trying to negate this statement and want to make sure I'm doing it right.
(p[tex]\vee[/tex]q) ---> (p [tex]\wedge[/tex] q)

So I don't negate both sides do I or else that would just make them equal out again? So I just negated the left side, so [tex]\neg[/tex](p[tex]\vee[/tex]q) is equivalent to [tex]\neg[/tex]p[tex]\wedge[/tex][tex]\neg[/tex]q

So that's the answer I got:
[tex]\neg[/tex]p[tex]\wedge[/tex][tex]\neg[/tex]q ---> (p [tex]\wedge[/tex] q)
 
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  • #2
p=>q = ~p or q

Using de morgans law : ~(p=>q) = ~(~p or q) = p and ~q

So ~(p or q implies p and q) = p or q and ~(q and p) -> p or q and ~q or ~p -> p xor q
 
  • #3
Sorry I am new to all this and what you have up there is very confusing. I can't really tell what's going on and what the final answer is. Anyway you can use the actual math symbols and break the steps into separate lines? I'd really appreciate it :)
 
  • #4
JonF's already done too much work for you. It's against the forum rules to simply do the problems for you. You're supposed to work them out yourself.

Use the fact that you can write p→q as (~p)∨q. The latter form is easier to see how to negate.
 
  • #5
Ya you're right sorry..I was just having a hard time understanding the symbols he was using but I think I got it now..so the final answer I got was:

(p v q) ^ (~p v ~q)

Is this what you had?
 
  • #6
That's correct. You can simplify it a bit if you want.
 

1. What does it mean to "negate" an "if then" statement?

Negating an "if then" statement means to find the opposite of the original statement. This is done by changing the truth value of the statement. For example, if the original statement is "If it is raining, then the ground is wet," the negation would be "If it is raining, then the ground is not wet."

2. How is a negated "if then" statement represented symbolically?

In symbolic logic, the negation of an "if then" statement is represented by placing a negation symbol (~) in front of the statement. For example, the negation of "If it is raining, then the ground is wet" would be "~(If it is raining, then the ground is wet)."

3. What is the truth value of a negated "if then" statement?

The truth value of a negated "if then" statement depends on the truth value of the original statement. If the original statement is true, then the negation will be false. If the original statement is false, then the negation will be true.

4. Can a negated "if then" statement be simplified?

Yes, a negated "if then" statement can be simplified using logical equivalencies. For example, ~(P→Q) is logically equivalent to (P ∧ ~Q). This means that the original statement can be simplified to "P is true and Q is false."

5. How is negation used in logical reasoning?

Negation is an important tool in logical reasoning as it allows us to consider alternative possibilities and evaluate the strength of an argument. By negating an "if then" statement, we can examine the validity of the original statement and determine whether it holds in all cases or not.

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