# Dividing a number by zero

Discussion in 'Physics & Math' started by chikis, Mar 10, 2013.

1. ### chikisRegistered Senior Member

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328
Who can help me solve this problem:

(0 * P) + 6 = 5
Make P the subject of the formular. Thank you.

3. ### NehushtanRegistered Member

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That equation is equivalent to $6=5$ which is false regardless of the value of $P$.

5. ### Prof.Laymantotally internally reflectedRegistered Senior Member

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I thought it was equal to 0 = -1, in that case there is no solution for P, or it is no reals.

7. ### PeteIt's not rocket surgeryRegistered Senior Member

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All false statements are equivalent.

Starting from anything false (like (0 * P) + 6 = 5), you can conclude anything at all (eg 6=5, 0=-1, or even "Your mama's not fat.")

8. ### eramSciengineerValued Senior Member

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Actually, I think P is -∞.

(0*(-∞))+6 = -1 + 6 = 5

Of course it can produce any other answer but its the only "value" that fits.

9. ### PeteIt's not rocket surgeryRegistered Senior Member

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Ew, I need to scrub my eyes.
.

10. ### eramSciengineerValued Senior Member

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that's if you're trying to solve for P. you get P = -1/0

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12. ### James RJust this guy, you know?Staff Member

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$0 \times P = 5 -6 = -1$

$P = -1/0$

///ERROR Will Robinson. ERROR!

Division by zero.

Does not compute.

Core dump follows: 0394048583743FAB43949CD3940390AAA3485401285405885...

Dave, my mind is going. I can feel it. I ... can ... feel ... it.

Would you like me to sing you a song, Dave?

xxx Blurk Kerching.

13. ### eramSciengineerValued Senior Member

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1,877
and......boom.

14. ### NehushtanRegistered Member

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And $\frac{-1}0$ does not exist. It is NOT $-\infty$; it simply does not exist.

15. ### SecretRegistered Senior Member

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This thread fully account of the various division by zero issues contributed by many users. It also briefly talk about infinity. The only thing it does not account for is whether there is a proof on every conceivable number system involving division by zero must end with contradictions

Took ages to find the thread because the search function does not search any threads beyond a year ago (return only my latest two threads), which I am not sure whether its a bug or intended

Therefore there exist no P in (R or C or Q etc.) such that (0 * P) + 6 = 5 is true

16. ### eramSciengineerValued Senior Member

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What do you mean by "exist"? How do you define it?

17. ### KitemanSARegistered Senior Member

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Sorry, his equation was correct. Anything except zero, when divided by zero equals infinity with the appropriate sign. 0/0 and infinity*0(and their inverses) are undefined.

18. ### rpennerFully WiredValued Senior Member

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4,833
"Exist" in this context means "is a number in a logically well-defined system"

Even in systems with numbers bigger than any finite numbers, transfinite numbers, multiplying any number by zero is still zero.

Introducing a "reciprocal" of zero breaks arithmetic in many ways.

$\color{red} 1 = 0 \times \infty = 0^2 \times \infty = 0 \times ( 0 \times \infty ) = 0 \times 1 = 0 N = ( M - 1 ) + (N + 1 - M ) = [ ( (M - 1) \times \infty ) + ( ( N + 1 - M ) \times \infty ) ] \times 0 = ( ( M - 1 ) \times \infty ) \times 0 + 0 \times ( ( N + 1 - M ) \times \infty ) = ( ( M - 1 ) \times 1 ) + ( 0 \times \infty ) = M$

// Edit -- the red in the above mathematics was used to show that the above trains of symbols are Contradictions and reasons why the reciprocal of zero is not a number

Last edited: Mar 11, 2013
19. ### KitemanSARegistered Senior Member

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It only breaks if you try to define 0/0 or its inverse varients.

20. ### GeoffPCaput gerat lupinumValued Senior Member

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I don't see the point of all this. I could make up any factorial illogical premise - even make the initial assertions exclusive of each other, and then claim they're not, and post a fucked up Venn diagram. So what? Why waste time with it?

21. ### originHeading towards oblivionValued Senior Member

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So since you say $\frac{-1}{0} = -\infty$.

Does that mean $-\infty \times 0 = -1$?

Last edited: Mar 12, 2013
22. ### NehushtanRegistered Member

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$\lim_{x\to0^-}\frac{-1}{x}=+\infty$ whereas $\lim_{x\to0^+}\frac{-1}{x}=-\infty$ So $\frac{-1}{x}$ goes in different directions depending on which side of 0 we approach. Hence $\lim_{x\to0}\frac{-1}{x}$ does not exist.

You are right in that $0/0$ is not defined. But $-1/0$ is not $-\infty$ and neither is $1/0$ equal to $\infty$. This is an all too common mistake – and what’s more, people should stop writing things like $-1/0$ and $1/0$ and treating them as numbers (which they’re not).

Perhaps you’re thinking of $\lim_{x\to\infty}\frac1x=0$ and $\lim_{x\to-\infty}\frac{-1}x=0$. These limits exist. However $\lim_{x\to0}\frac{\pm 1}{x}$ do not exist (see above). If you’d only avoid writing the first two limits as $1/\infty=0$ and $-1/-\infty=0$ (which really you shouldn’t) then you wouldn’t be fooled into thinking that $1/0=\infty$ and $-1/0=-\infty$.

23. ### PeteIt's not rocket surgeryRegistered Senior Member

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Tex Tip:
In tex, "x" shows as a cursive letter x, and so shouldn't be used for a multiplication symbol. Use \times instead.
$7 \times 6 = 42$​