The problem with dividing zero by zero (video) | Khan Academy (2024)

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  • Wilbur Donovan

    12 years agoPosted 12 years ago. Direct link to Wilbur Donovan's post “Is 0/0 = 1? Or is it unde...”

    Is 0/0 = 1? Or is it undefined?

    Couldnt you say that the numbers are like a dimension where you could join the infinitys'?

    Like for example, if you wrote a number line on a piece of paper, with positive infinity at the top and negative infinity at the bottom, couldn't you fold the paper so that negative and positive infinity are the same?

    (45 votes)

    • Paul Moore

      12 years agoPosted 12 years ago. Direct link to Paul Moore's post “0/0 is undefined. If sub...”

      The problem with dividing zero by zero (video) | Khan Academy (4)

      The problem with dividing zero by zero (video) | Khan Academy (5)

      The problem with dividing zero by zero (video) | Khan Academy (6)

      0/0 is undefined. If substituting a value into an expression gives 0/0, there is a chance that the expression has an actual finite value, but it is undefined by this method. We use limits (calculus) to determine this finite value. But we can't just substitute and get an answer.

      Example: the limit as x approaches 0 of x/x = 1, but the expression x/x is undefined at x = 0.

      In geometry, we do not consider lines to meet at infinity. We consider them to go on forever in opposite directions, never meeting. In physics, of course, space is curved, and a real "line" might, in fact, be a closed figure (which is somewhat like "meeting at infinity")... but not in geometry.

      Your thinking is great - keep it up.

      (56 votes)

  • Paulius Eidukas

    11 years agoPosted 11 years ago. Direct link to Paulius Eidukas's post “In my opinion, it seems t...”

    In my opinion, it seems that 0/0 could be equal not only to 0 and/or 1, but actually to any number.

    Let's say that 0/0 = x
    Following the principles of division and multiplication, we can re-arrange the equation like this:
    0x = 0
    From here it becomes obvious that this equation is true for any x, because 0 multiplied by anything is still equal to 0:
    0 * 0 = 0; 0/0 = 0
    0 * 1 = 0; 0/0 = 1
    0 * 2 = 0; 0/0 = 2
    ... and so on

    Is this also a valid way to prove that 0/0 is indeterminate?

    (34 votes)

    • David

      10 years agoPosted 10 years ago. Direct link to David's post “I'm just stating what Sal...”

      The problem with dividing zero by zero (video) | Khan Academy (10)

      I'm just stating what Sal said in the video, but some people say that 0/0 is obviously 0, since 0/4, for example, is zero. They say zero divided by anything is zero. However, some say anything divided by zero is undefined, since 4/0 and 5/0 are and so on. Others say that 0/0 is obviously one because anything divided by itself, just like 20/20 is 1. All of these points of view are logical and reasonable, yet they contradict each other. These statements are impossible and don't work, since a mathematical expression consisting of only constants (numbers like 1, not variables like x and y) can only have one value. These thoughts can not merge, as 0 is not 1 or undefined, and vice versa. So 0/0 must be undefined.

      Also, if you think about it more closely, (Sal also says this in the next video.) division must be able to be undone by multiplication. For example, 6 divided by 2 is 3, and it can be undone by multiplying 2 by 3 to get 6. If 0/0 is 1, then 1 times 0 is , so it is correct. If 0/0 is 0, then 0 times 0 is 0, so it is also correct. If 0/0 is undefined, then you can't multiply back. The first two can not be proved false using this method, nor can the latter, since it is not exactly defined as division anyway.

  • Christine Moreda

    7 years agoPosted 7 years ago. Direct link to Christine Moreda's post “If we have something and ...”

    If we have something and we divide it by 2, then don't we separate it into two pieces?
    And if we have something and divide it by 1, then don't we "separate" it into one piece?
    So if we have something and divide it by 0, wouldn't that be like making it disappear?
    Wouldn't that be impossible, rather than undefined?
    To take a thing and turn into nothing?
    (So, my first hypothesis is that dividing by zero is not undefined, but is defined as impossible.)

    (Now, to look at what we mean by "divide" or if we actually mean more than one thing.)
    Divide (per somewhere online, I read), means to calculate how many times we could add one number to itself to get another number.
    (For example, 10/5 = 2. We add 5 to itself 2 times to get 10.)

    So with two divided by zero, we could continue adding zero to itself forever, but still not get to two.
    Doesn't that make 2/0 impossible, not undefined?

    1/3 says you have 1 number of thirds.
    So with 3/0, would you have 3 number of "0ths"...
    I've never heard of a "0th" and I don't think they exist.
    0 (zero) of a pie is 0.
    1/3 of a pie is 1/3.
    1/2 of a pie is 1/2.
    1/1 of a pie is a whole.
    1/0 of a pie?

    Since dividing by zero (i.e. having a "zeroth" as a denominator), I think, is impossible, then there is no such thing as a zeroth of a pie.

    On a similar note, if you say you have zero halves (0/2),
    Or you say you have zero thirds (0/3)
    Then you have zero of those things.
    But you could also read those as zero divided by two (0/2)
    Or zero divided by three (0/3)

    Divide (per some online definition) also means calculate how many times one number goes into another.
    With 10/5, 5 goes into 10 two times. So 10/5 = 2.
    But with 0/2, how does 2 go into 0?
    (So, now it seems that 0/2 is undefined!) (Though, using a different meaning of division, we know we can have zero halves and that that simply equals 0!)
    (So that is part of the reason why it seems to me that we are not being consistent in our meaning and usage of division, and that is affecting how we think about dividing by zero.)

    (So, to restate my main point...)
    I think that dividing by zero, regardless of what you mean by "divide," is impossible.
    So next would be why this classic example meant to show that we can't divide by zero is actually flawed:
    a/0 = b

    Each side is multiplied by 0 in order to prepare to cancel out the zeros, like this:
    (a/0) x 0 = b x 0

    The problem with this is that a/0 is impossible, so when the zeros are "cancelled," what's really getting cancelled (on the left side) (along with the zero we added) is a part of an impossible number. If the number is impossible, then who are we to take a part of it out (the zero), and assume the remaining part is valid?
    It is the entire number a/0 that is impossible, not just the 0 at the bottom.

    So, if a/0 = b, and a/0 is impossible, then it seems that b is impossible too.

    I've yet to finish a review of imaginary numbers and how they are used, while keeping the above in mind.
    But I wonder if this is normal practice -- to pick and choose which parts of impossible things we use and which we don't. It seems that would really mess up our math.

    I'm curious how this applies to the study of more advanced math, science, and astronomy.
    Any thoughts on dividing by zero, or any of this?

    4/10/17 I corrected this post and would love to hear/read anyone's thoughts on it!

    (18 votes)

    • Jubjub Bird

      7 years agoPosted 7 years ago. Direct link to Jubjub Bird's post “1. Separating into n piec...”

      1. Separating into n pieces means that you need n new pieces to get the original piece. If you separate into 0 pieces means that you need 0 of the new piece/s to get to the original 1. In other words, you're trying to find- meaning define- a number that when multiplied by zero you get 1. Which is impossible.
      Note that I didn't call p/0 impossible. I called it impossible to define, which is why it's undefined.

      2. (No 2, because in the question it's just a definition)

      3. When you say "forever", it means that you would have to add an infinite amount of 0's to get to 2. But doing that would only give you 0, meaning you'll need to add a few more zeros- another infinite amount- and you'll stay at zero. And you keep going, and staying at zero. So yeah, it is impossible- impossible to define it's answer.

      4-5. Interesting way of looking at it. But that doesn't prove that it's not undefined.

      6. 0/p is 0, just like you say.

      7. 2 does go into 0, just like it goes into 1 and into 0.3. in fact, it goes into 0 better than into them! Into zero it goes exactly 0 times (a whole number), but into 1 it goes only a half time and into 0.3 it goes only 0.15 times (both are fractions).

      8-11. The flaw in your logic is that you aren't allowed to multiply by 0 when solving equations.

      12. I don't know what to say about this, because I don't know anything about imaginary numbers.

      13. I also don't know much about how this relates to more advanced math, science, and astronomy.

      4/26/17 I re-answered to the corrected post, and I still say the following:
      Thoughts. Mathematicians are really comfortable with it being undefined, and they really don't have any motivation to change that.

      (2 votes)

  • phineartsacademy

    a year agoPosted a year ago. Direct link to phineartsacademy's post “I'm just thinking about w...”

    I'm just thinking about why x/x=1. Division is repeated subtraction. 10/5=2 cause 10-2-2-2-2-2=0. You subtract 2 five times from ten to get zero. You subtract ten one time from ten to get zero. You subtract zero zero times from zero to get zero. Therefore, 0/0=0. And then it works in reverse. 0*0=0. And the rule x/0=0 isn't broken. x/x=1 is ignored, but I already explained why. Also, it makes sense because zero isn't a number. Zero is a symbol that represents nothing. And nothing is undefined.

    (6 votes)

    • Venkata

      a year agoPosted a year ago. Direct link to Venkata's post “Zero isn't a symbol. It i...”

      The problem with dividing zero by zero (video) | Khan Academy (17)

      Zero isn't a symbol. It is a number just how 1 or 45 is. Just how every number tells us the existence of something, zero tells us the existence of nothing.

      As for 0/0, you can't define it as 0 because a lot of problems arise, some of which are far beyond the current scope here, and will be dealt with in a really interesting branch of Mathematics called Calculus.

      And to add on, there's a reason why your logic doesn't work. So, okay, suppose we say 0/0 is 0. What is 0/1? That's also 0. What about 0/2? That's also zero. 0/1 = 0 says "I subtract 0 from 0 one time to get 0". 0/2 = 0 says "I subtract 0 from 0 twice to get 0". These are fair statements to make. But, subtracting 0 from 0, 0 times is a bit absurd, as that's similar to not doing anything at all. So, the idea of division being repeated subtraction breaks down.

      Finally, I'll leave you with this. 0/0 has a special name in the context of limits. It's called an indeterminate form, and it pops up a lot in advanced Math, along with other indeterminate forms like infinity/infinity. Just know that 0/0 can be any number you want it to be. Think of it like this. Let 0/0 = x. So, we have x * 0 = 0. Now, what value of x satisfies this equation? Well, any number does! That's why 0/0 can be any number, but in the future, you'll learn methods to narrow down what number it is, as you'll need it to solve problems!

  • mk

    4 years agoPosted 4 years ago. Direct link to mk's post “Imagine having 0 cookies ...”

    Imagine having 0 cookies to give among 0 friends. How many cookies would each person get? See, it doesn`t make sense. And the cookie monster is sad that you have 0 cookies, and you are sad that you have 0 friends.

    (11 votes)

  • Redapple8787

    7 years agoPosted 7 years ago. Direct link to Redapple8787's post “From what I understand, w...”

    From what I understand, whenever mathematicians can't find a good answer for something, they leave it undefined. Do they leave things undefined quickly? How many undefined things are there in the world? Can undefined cases even exist?

    (6 votes)

    • David Severin

      7 years agoPosted 7 years ago. Direct link to David Severin's post “In real life, there is no...”

      In real life, there is no reason to divide something by nothing, as it is undefined in math, it has no real applications in the real world. But in theory, it can be undefined. Similarly, infinity is also just a concept in math, it cannot have a real application either, even if you ask how many atoms are in the universe, it is a certain number even though it might be a very large number. There are not a lot of undefined things in math, but all of Geometry is based on three undefined terms, a point, line and plane none of which can exist in the real world, but without the theory of these, real world applications would be more difficult. You act like having something undefined is just an arbitrary thing mathematicians do, it is not at all.

      (8 votes)

  • doo*shbag

    a year agoPosted a year ago. Direct link to doo*shbag's post “i think 0/0 is 0 bcs if u...”

    i think 0/0 is 0 bcs if u have zero friends and zero cookies how many cookies will each friend get?
    ZERO!

    (5 votes)

    • Kim Seidel

      a year agoPosted a year ago. Direct link to Kim Seidel's post “The Multiplication Proper...”

      The Multiplication Property of 0 tells us that any number times 0 = 0. If you turn that into an equation, you have:
      x*0 = 0, where "x" is any number.
      Solve the equation and your got x = 0/0. So, 0/0 can be made to equal any number. Since there is no single agreed upon solution, we say that 0/0 is indeterminate.

      (8 votes)

  • Brian Trzepacz

    5 years agoPosted 5 years ago. Direct link to Brian Trzepacz's post “If 0 x 5 = 0 then I divid...”

    If 0 x 5 = 0 then I divide both sides by 0, 0/0 = 5. So,
    0 x y = 0, y = 0/0, so nothing divided by nothing can be anything?

    (4 votes)

    • Kim Seidel

      5 years agoPosted 5 years ago. Direct link to Kim Seidel's post “Essentially, yes. This i...”

      Essentially, yes. This is why 0/0 is considered indeterminate - there is no single agreed upon solution.

      (5 votes)

  • JETTS JR.(TWS)

    9 months agoPosted 9 months ago. Direct link to JETTS JR.(TWS)'s post “how does he wright so wel...”

    how does he wright so well using a computer?

    (5 votes)

    • 10175842

      8 months agoPosted 8 months ago. Direct link to 10175842's post “no idea”

      no idea

      (3 votes)

  • T.J.King2002

    8 years agoPosted 8 years ago. Direct link to T.J.King2002's post “Could 0/0 be equal to ale...”

    Could 0/0 be equal to aleph-null?

    (6 votes)

    • Journey to TĐN 2022

      2 years agoPosted 2 years ago. Direct link to Journey to TĐN 2022's post “No, it can be anything. B...”

      No, it can be anything. Btw aleph null is undefined as it is an infinity(∞)

      (1 vote)

The problem with dividing zero by zero (video) | Khan Academy (2024)

FAQs

What will be the answer if we divide zero by zero? ›

In ordinary arithmetic, the expression has no meaning, as there is no number which, multiplied by 0, gives a (assuming a≠0), and so division by zero is undefined. Since any number multiplied by zero is zero, the expression 0/0 is also undefined; when it is the form of a limit, it is an indeterminate form. Q.

What is the problem with dividing zero by zero? ›

Another one can argue that 0/0 is ​1, because anything divided by itself is 1. And that's exactly the problem! Whatever we say 0/0 equals to, we contradict one crucial property of numbers or another. To avoid "breaking math," we simply say that 0/0 is undetermined.

Is 0 0 is infinity? ›

Uh, 0/0 doesn't equal infinity, it's UNDEFINED because if 0/0 = x, then x times 0 = 0, but that's true with every number.

When 0 is divided by any number, the answer is? ›

Any number divided by 0 is 0.

Is 1 0 undefined or infinity? ›

So, when the value of denominator tends to or equals to zero, then the value of the expression tends to or becomes so large that we cannot find it's bound or in others it becomes infinity i.e., 1/0=∞. Clear and simple!

Can you really not divide by zero? ›

These notes discuss why we cannot divide by 0. The short answer is that 0 has no multiplicative inverse, and any attempt to define a real number as the multiplicative inverse of 0 would result in the contradiction 0 = 1.

What is 1 infinity equal to? ›

Infinity is a concept, not a number. We know we can approach infinity if we count higher and higher, but we can never actually reach it. As such, the expression 1/infinity is actually undefined.

What equals infinity in math? ›

In Math, “infinity” is the concept describing something larger than the natural number. It generally refers to something without any limit. It is a state of endlessness or having no time, space, or other quantity limits. The common symbol for infinity, ∞, was invented by the English mathematician John Wallis in 1657.

Who invented zero? ›

Therefore it is said that Aryabhatta found zero.

Can 9 go into 0? ›

Asked by Lee Williams, student, Aldridge State High School on August 8, 1997: What is the answer to 9 divided by 0 on a high school level and university level. The answer to this question is that there is no answer. By this we simply mean that there is no number which, when multiplied by 0, gives you 9.

What is 3 divided by infinity? ›

Answer and Explanation:

Any number divided by infinity is equal to 0.

When dividing any number by zero gives zero? ›

Dividing 0 by any number will give us a zero. Zero will never change when you multiply or divide any number by it. For example, a person has zero toffees which are to be divided among 7 ( let's say) children.

Why is 1 divided by 0 infinity? ›

Note: We must remember that the value of 1 divided by 0 is infinity only in the case of limits. The word infinity signifies the length of the number. In the case of limits, we only assume that the value of limit x tends to something and not equal to something. So, we consider it infinity.

Does undefined mean infinity? ›

Answer and Explanation:

Undefined is that its value is unknown, or something that doesn't exist, but it can be achieved with factorization, but infinity means no end, that is, too large to have an end.

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