# Why does 13 divided by 0 not equal infinity?Watch

Announcements
This discussion is closed.
#1
Why does 13 divided by 0 not equal infinity? I really don't understand why?
My Maths teacher who has a PhD. in Mathematics told us. So basically I told my friend in another class, and she said it doesn't. So we both decided to have a bet on here on which one of us is right.

EDIT: stop repping me guys! I wanna keep my ruby's!
1
5 years ago
#2
It doesn't? pffft why wouldn't it?
0
5 years ago
#3
(Original post by tazmaniac97)
Why does 13 divided by 0 not equal infinity? I really don't understand why?
My Maths teacher who has a PhD. in Mathematics told us. So basically I told my friend in another class, and she said it doesn't. So we both decided to have a bet on here on which one of us is right.
is undefined
3
#4
(Original post by SiMan)
It doesn't? pffft why wouldn't it?

(Original post by TenOfThem)
is undefined
but my maths teacher who has a PHD said it would, why should I believe you and not him?
2
5 years ago
#5
(Original post by tazmaniac97)
Why does 13 divided by 0 not equal infinity? I really don't understand why?
My Maths teacher who has a PhD. in Mathematics told us. So basically I told my friend in another class, and she said it doesn't. So we both decided to have a bet on here on which one of us is right.
n/0 is undefined; there's no answer as it doesn't make mathematical sense.
1
#6
(Original post by Strangey)
n/0 is undefined; there's no answer as it doesn't make mathematical sense.
who says it doesn't make mathematical sense, it makes perfect mathematical sense to me.
0
5 years ago
#7
(Original post by tazmaniac97)
but my maths teacher who has a PHD said it would, why should I believe you and not him?
Well if he says cows are birds would you believe him because he is a PhD? Ask him to prove it then.
9
5 years ago
#8
(Original post by tazmaniac97)
who says it doesn't make mathematical sense, it makes perfect mathematical sense to me.
How does it make perfect sense? 0 x infinity does not give you 13.....

Posted from TSR Mobile
9
5 years ago
#9
(Original post by tazmaniac97)
who says it doesn't make mathematical sense, it makes perfect mathematical sense to me.
The real numbers are defined as a field along with several other properties which don't matter for this. Using just the properties of a field, we can show that 0 has no multiplicitive inverse as follows-

Assume 0^(-1)=k

Then 0*k=1 (property of inverses)

so (0+0)*k=1 (0 is the additive identity)

so 0*k+0*k=1 (distributive property)

so 1+0*k=1 (by 2nd line)

so 0*k=0 (take 1 from both sides)

which is a contradiction since 0 does not equal 1.
13
5 years ago
#10
One thing you can sometimes do to try and get an understanding of things which aren't defined is to take limits. For example the limit as x->0 of x/x is 1, and the limit as x->0 of 1/x^2 is infinity, but the limit of 1/x as x->0 does not exist. To see this let x->0 from above (so x is always positive) and you get infinity. Also let x->0 from below, so you get -infinity. Since a limit must have only 1 value, it cannot exist in this case.
1
5 years ago
#11
he said it is to shut u up hahahhaa.

n/0 is mathematically undefined.

You can have n/m say, where m-->0

and say when m tends to 0 then n/m tends to infinity, but at m=0 n/m is not defined, ie it's meaningless writing such a thing!

Hope that helps

Posted from TSR Mobile
0
5 years ago
#12
(Original post by tazmaniac97)
who says it doesn't make mathematical sense, it makes perfect mathematical sense to me.
From the age 5 up until about 15, I thought infinity made perfect 'mathematical sense' to me. And then I started to find out about the actual maths, and realised I really didn't have a clue. Don't be fooled by what seems like common sense...
0
5 years ago
#13
(Original post by tazmaniac97)
who says it doesn't make mathematical sense, it makes perfect mathematical sense to me.
It probably makes little mathematical sense because you don't know that much about mathematics. Sounds harsh, but in this case I'm afraid it is true. I don't claim to be especially knowledgeable, but at least I looked at the wikipedia and wolfram mathworld pages on this.

Suppose
This implies that where . And I really hope you can see why that doesn't make sense.
2
5 years ago
#14
If you had an infinite number of nothing, you'd still have nothing, you wouldn't magically get numbers coming out of nowhere Therefore it's undefined
1
5 years ago
#15
(Original post by tazmaniac97)
but my maths teacher who has a PHD said it would, why should I believe you and not him?
Do not worry, I am a professor Emeritus from Harvard in mathematics, therefore the mathematical validity of my statement supercedes that of your mathematics teacher's.

Either you are misquoting him and he said something like "as x gets really small from the RHS, 13/x tends to infinity" or he shouldn't have a PhD in maths if he makes a mistake like this.

13/0 just like 1/0, 2/0, ... , a/0 is undefined.
0
5 years ago
#16
What he said ^. Saying 1/0 equals infinity is like saying an infinite amount of nothing will give you something. It simply does not make sense.
0
5 years ago
#17
There's SO many YouTube videos on dividing by zero... Numberphile actually found that it could actually equal anything you like, and they came up with a proof to show it.
0
#18
(Original post by SiMan)
Well if he says cows are birds would you believe him because he is a PhD? Ask him to prove it then.
But if he said that then there must be a good reason for it, so I would believe him
0
#19
(Original post by 2710)
How does it make perfect sense? 0 x infinity does not give you 13.....

Posted from TSR Mobile
Yeah but if I applied your logic to this situation, then...
13 x 0 = 0
so why doesn't 0 divided by 0 equal 13
0
5 years ago
#20
(Original post by tazmaniac97)
Yeah but if I applied your logic to this situation, then...
13 x 0 = 0
so why doesn't 0 divided by 0 equal 13
2
X
new posts
Latest
My Feed

### Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

### See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

### University open days

• SOAS University of London
Wed, 29 May '19
• University of Exeter
Thu, 30 May '19
• Cranfield University
Cranfield Forensic MSc Programme Open Day Postgraduate
Fri, 31 May '19

### Poll

Join the discussion

Loved the paper - Feeling positive (221)
22.97%
The paper was reasonable (430)
44.7%
Not feeling great about that exam... (174)
18.09%
It was TERRIBLE (137)
14.24%