# Some Logic equation

• ٩๏̯͡๏۶
• Posts: 3423
• Loc: Richland, WA

3+ Months Ago

If A then B, if not B then not A.

Can this statment be proven false?
• Brewmaster
• Posts: 6296
• Loc: Seattle, WA

3+ Months Ago

Nope. It's a core concept in classical logic:
http://en.wikipedia.org/wiki/Modus_tollens

However, the way you've written it is incorrect. Get rid of the second "if". The form is:

If A, then B.
Not B.
Therefore, not A.
• Moderator
• Posts: 8747
• Loc: Aberdeen, Scotland

3+ Months Ago

Are you two drunk?
• Brewmaster
• Posts: 6296
• Loc: Seattle, WA

3+ Months Ago

Not yet.
• Moderator
• Posts: 8747
• Loc: Aberdeen, Scotland

3+ Months Ago

Haha, good answer. I've only had one beer (a Mexican one) and not in the slightest bit feeling it, however after seeing the first couple of posts here i did start to think if things were starting to get to me.

I apologise for taking away from what should be a very interesting topic
• ٩๏̯͡๏۶
• Posts: 3423
• Loc: Richland, WA

3+ Months Ago

spork wrote:
Nope. It's a core concept in classical logic:
http://en.wikipedia.org/wiki/Modus_tollens

However, the way you've written it is incorrect. Get rid of the second "if". The form is:

If A, then B.
Not B.
Therefore, not A.

Ah, thanks spork
• brego from LA
• Posts: 2852

3+ Months Ago

SB wrote:
Haha, good answer. I've only had one beer (a Mexican one) and not in the slightest bit feeling it, however after seeing the first couple of posts here i did start to think if things were starting to get to me.

I apologise for taking away from what should be a very interesting topic

what brand did you drank?
• Newbie
• Posts: 7

3+ Months Ago

what did you smoke?))
• Genius
• Posts: 13511
• Loc: Florida

3+ Months Ago

If "is dead", then "it decomposes".
Not "decomposing".

This would mean that when you die, you are no longer dead if you're frozen afterwards.
• Genius
• Posts: 8485
• Loc: USA

3+ Months Ago

If "is dead", then "it stinks".
Not "stinking".

That is a bit flawed, but then again the reaction "stink" doesn't occur right after the action "dead". The "stink" is the reaction to the action "decompose".

Just thought I'd bring this up.
• Brewmaster
• Posts: 6296
• Loc: Seattle, WA

3+ Months Ago

I think you're confusing validity with soundness
• Genius
• Posts: 13511
• Loc: Florida

3+ Months Ago

I guess an easy way to understand it is to use stepping stones.

There are two stones extending out from the shore. A is closest to the shore, and B is the next step out from A.

If "traveled to B", Then "passed through A".
Not "passed through A".
Therefore, "not traveled to B".

If you have to step on the A stone in order to get to the B stone, there's no way you could have been on the B stone if you never went through the A stone. This of course, ignores things like swimming around the A stone to get to the B stone though.
• Moderator
• Posts: 8747
• Loc: Aberdeen, Scotland

3+ Months Ago

labrego wrote:
SB wrote:
Haha, good answer. I've only had one beer (a Mexican one) and not in the slightest bit feeling it, however after seeing the first couple of posts here i did start to think if things were starting to get to me.

I apologise for taking away from what should be a very interesting topic

what brand did you drank?

I think it was called "XX". I drank another Mexican beer before and was sure that was the name, but this "XX" didn't taste as nice as i thought. It was still good, but not as good. Is there a similar named Mexican beer out there?
• Brewmaster
• Posts: 6296
• Loc: Seattle, WA

3+ Months Ago

XX is better than Corona, that's for sure Then again, I don't generally drink light lagers except for German hefeweizens and pilseners.
• Proficient
• Posts: 351
• Loc: Indiana, USA

3+ Months Ago

If "Beer," then "German."
XX is not "German,"
Therefore, XX is not "Beer."

*wink*

A perfect syllogism - but the underlying statement is not factual. True statements are always logical, but logical statements are not always true. Or, to put it another way: there is plenty of totally good non-German beer.
• Newbie
• Posts: 7

3+ Months Ago

i think there's some mis-logic in "dead" thing..
• Brewmaster
• Posts: 6296
• Loc: Seattle, WA

3+ Months Ago

I'll just leave these here:

http://en.wikipedia.org/wiki/Validity
http://en.wikipedia.org/wiki/Soundness
• Genius
• Posts: 13511
• Loc: Florida

3+ Months Ago

All but one truth will one day be proven wrong. Or, as UNFLUX used to say, the only constant is change.

Some people say you can't divide by zero, I ask, what happens to the thing that was supposed to be divided, where does it go ?
• Proficient
• Posts: 351
• Loc: Indiana, USA

3+ Months Ago

joebert wrote:
All but one truth will one day be proven wrong.

Including that. *wink*
• Super Moderator
• Posts: 23469
• Loc: Woodbridge VA

3+ Months Ago

I love logic. It was my favorite college class. I still have the book in a box in storage somewhere.
• Brewmaster
• Posts: 6296
• Loc: Seattle, WA

3+ Months Ago

joebert wrote:
Some people say you can't divide by zero, I ask, what happens to the thing that was supposed to be divided, where does it go ?

It doesn't "go" anywhere. You can't divide by zero in the first place; it has no mathematical meaning to do so.
• Genius
• Posts: 13511
• Loc: Florida

3+ Months Ago

Quote:
It doesn't "go" anywhere. You can't divide by zero in the first place; it has no mathematical meaning to do so.

I start out with an empty room that I want to divide into zero equal spaces. I still have an empty room even if it wasn't divided, don't I ?

I can't simply forget the left operand existed, just because there was nowhere to send it.

If it's not possible to divide by zero, why do programming languages have error handlers for when it happens ?
• Super Moderator
• Posts: 23469
• Loc: Woodbridge VA

3+ Months Ago

Quote:
My teacher says you can't divide a number by zero. Why?

Let's look at some examples of dividing other numbers.

10/2 = 5 This means that if you had ten blocks, you could
separate them into five groups of two.

9/3 = 3 This means that if you had nine blocks, you could
separate them into three groups of three.

5/1 = 5 Five blocks could be separated into five groups
of one.

5/0 = ? Into how many groups of zero could you separate
five blocks?

It doesn't matter how many groups of zero you have, because they would never add up to five since 0+0+0+0+0+0 = 0. You could even have one million groups of zero blocks, and they would still add up to zero. So, it doesn't make sense to divide by zero since there is not a good answer.

If you know a little bit about multiplication, you could look at it this way:

10/2 = 5 This means that 5 x 2 = 10

9/3 = 3 This means that 3 x 3 = 9

5/1 = 5 This means that 5 x 1 = 5

5/0 = ? This would mean that the answer x 0 = 5, but
anything times 0 is always zero.

- Dr. Margaret

Credit

If you didn't know that, after watching this video, you'll never forget it...

• ٩๏̯͡๏۶
• Posts: 3423
• Loc: Richland, WA

3+ Months Ago

Quote:
10/2 = 5 This means that if you had ten blocks, you could
separate them into five groups of two.

When I read that I was epecting them to say you "separated them into two groups of five.

Did anyone else expect this, or have I been think of division the wrong way for my entire life?

I know they are the same thing but, I wonder how others seperate them out.

Same with this:
Quote:
5/1 = 5 Five blocks could be separated into five groups
of one.

When I read that I think one group of five.
• Brewmaster
• Posts: 6296
• Loc: Seattle, WA

3+ Months Ago

joebert wrote:
I start out with an empty room that I want to divide into zero equal spaces. I still have an empty room even if it wasn't divided, don't I ?

I can't simply forget the left operand existed, just because there was nowhere to send it.

If it's not possible to divide by zero, why do programming languages have error handlers for when it happens ?

You're not thinking about it correctly. The dividend doesn't "need to go anywhere" because you're not doing anything to it in the first place. A room that is never divided by anything is still the same room. And since division by zero has no meaning, you're never doing a division.

Programming languages have handlers for such an error because trying to divide by zero is an error. To not treat it as such would break mathematics and cause your dearest loved ones to catch on fire.
• Genius
• Posts: 13511
• Loc: Florida

3+ Months Ago

Error handlers are designed to keep the program from crashing in cases the programmer hasn't figured out how to deal with yet.

If the equation exists, there has to be a way to solve it.

zero divided by anything is universally accepted to result in zero. Why does that work, and why can't anything divided by zero result in the original anything being returned ?

0 / 1 = 0
1 / 0 = 1
• Super Moderator
• Posts: 23469
• Loc: Woodbridge VA

3+ Months Ago

joebert wrote:
Error handlers are designed to keep the program from crashing in cases the programmer hasn't figured out how to deal with yet.

If the equation exists, there has to be a way to solve it.

zero divided by anything is universally accepted to result in zero. Why does that work, and why can't anything divided by zero result in the original anything being returned ?

0 / 1 = 0
1 / 0 = 1

I think I actually have to agree with you on this one. Semantically speaking, if you substitute the word nothing for the number zero, any number divided by nothing equals the original number because there is no division taking place. From a mathematical view I know that's wrong, but it certainly makes sense to me.
• Brewmaster
• Posts: 6296
• Loc: Seattle, WA

3+ Months Ago

joebert wrote:
Error handlers are designed to keep the program from crashing in cases the programmer hasn't figured out how to deal with yet.

If the equation exists, there has to be a way to solve it.

zero divided by anything is universally accepted to result in zero. Why does that work, and why can't anything divided by zero result in the original anything being returned ?

0 / 1 = 0
1 / 0 = 1

Because if A / B = C, then it must follow that C * B = A.

In the equation D / 0 = E, there is no number E that, when multiplied by zero, gives a non-zero number D.

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