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.9999...=1

  • Thread starter Thread starter Josepho1997
  • Start date Start date
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Josepho1997

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I've been told that .999...=1 (.999... means .9999 repeating)
What do you think? Does. 9999=1?
 
jhawkkw said:
Following the same set if steps, you would end up with 9x =2. Thus x =2\9, which is indeed what. 2222222..... is equal to.
Click to expand...
Tell me if I'm wrong here:
x=.22222222......
10x= 2.22222222......
10x-x=9x 2.22222222.....-.2222222222= 2
2=9x
divide each side by 9
2/9=x
x=.2222222222222
back to where we started


ah, I think I get it...
.99999999.....would be the only number equal to 1?:confused:
 
Mikestony said:
Tell me if I'm wrong here:
x=.22222222......
10x= 2.22222222......
10x-x=9x 2.22222222.....-.2222222222= 2
2=9x
divide each side by 9
2/9=x
x=.2222222222222
back to where we started


ah, I think I get it...
.99999999.....would be the only number equal to 1?:confused:
Click to expand...

Correct, it is an odd situation that comes up in mathematics. There others out there too, but I will spare everyone the messy details because the proofs involve higher mathematics and aren't easy to type. This method shown above can be used to figure out the fraction for any repeating decimal. Pretty nifty I'd say.
 
I like how one of the tags is "trolls." o.o

This was an awesome thread. Great read. It makes total sense.
 
It depends on the setting really. If your manufacturing gears with a wire edm then .9999 is still .0001 underside from 1.00000. now if you have a geometric tolerance of lets say +- .00001 than that dimention being at .9999 would bring you out of tolerance by .00009 rendering the part non conforming and scrap.
 
h4x0rj3ff said:
It depends on the setting really. If your manufacturing gears with a wire edm then .9999 is still .0001 underside from 1.00000. now if you have a geometric tolerance of lets say +- .00001 than that dimention being at .9999 would bring you out of tolerance by .00009 rendering the part non conforming and scrap.
Click to expand...

Partially true. .9999 itself is not equal to 1. But the idea behind the question and the proof is for .9999...., meaning repeating infinitely forever and is absolutely 100% true.
 
It's been said already, but it's true.

You can also see it even more easily like this:

(1/3) + (1/3) + (1/3) = 1

0.3333... + 0.333333... + 0.333... = 1

Therefore

0.999999..... = 1



It also works with other numbers that end with a decimal periodic 9. Such as:
23.56999999.... = 23.57
 
DaSchmarotzer said:
It's been said already, but it's true.

You can also see it even more easily like this:

(1/3) + (1/3) + (1/3) = 1

0.3333... + 0.333333... + 0.333... = 1

Therefore

0.999999..... = 1



It also works with other numbers that end with a decimal periodic 9. Such as:
23.56999999.... = 23.57
Click to expand...

thats only true if you assume 0.3333... = 1/3
which (depending on context, may or may not be true




mikedt said:
2+2=3
Click to expand...

There are 10 types of people in the world.. those that count in binary, and those that don't.
 
psionandy said:
thats only true if you assume 0.3333... = 1/3
which (depending on context, may or may not be true
Click to expand...

1/3 is exactly = .333... repeated for ever and you can easily discover that for yourself by dividing 1 by 3. If you do it manually using the standard you will constantly get repeating 3's forever until you decide you've had enough punishment.

I wanted to avoid the use of higher mathematics, but the reason behind the equality is stated right in the wiki article:

The equality of 0.999... and 1 is closely related to the absence of nonzero infinitesimals in the real number system, the most commonly used system in mathematical analysis.
Click to expand...
Furthermore:
The equality 0.999... = 1 has long been accepted by mathematicians and is part of general mathematical education. Nonetheless, some students find it sufficiently counterintuitive that they question or reject it, commonly enough that the difficulty of convincing them of the validity of this identity has been the subject of several studies in mathematics education
Click to expand...
Whether anyone chooses to accept it or not is their choice, but nonetheless, it is 100% true. I often run into non-believers when I teach this topic in the Infinite Series part of Calculus II, granted the proof for that class is different giving the context of the class.
 
I could give you the real reason, but would require the use of real analysis which is usually a 4th year mathematics course. As I stated earlier, it has to deal with the fact that there is no non-zero infinitesimal between .999... and 1.0. In other words, there is no number between .999... and 1.
For the purpose of a proof, lets assume they are distinct numbers. For any number not ending in a infinite sequence of 9's, you can always find another number in between two different numbers by simply finding the midpoint (x1+x2)/2. This doesn't work with numbers ending in the infinite sequence of 9's because the midpoint between .9 and 1 is .95. so if you could take the midpoint of the two, following that idea, the last number would have to be a 5, which contradicts the whole notion because .999 is an infinite sequence of 9's and would actually be greater than our midpoints. This creates an absurdity, which many mathematicians call a proof by contradiction. So since our original idea about them being two different numbers let to a contradiction, that means that assumption must be false, and thus means they have to be the same number.
 
Without a doubt .999 =1 it can be mathematicaly proved as shown above. .222 does not =1 nor does .3333 .444 etc. Again all this was said above but i thought i would verify it.
 
jhawkkw said:
1/3 is exactly = .333... repeated for ever and you can easily discover that for yourself by dividing 1 by 3. If you do it manually using the standard you will constantly get repeating 3's forever until you decide you've had enough punishment.
.
Click to expand...


well.. in that case pie is 3.14 :p

or whatever number you get before you decide you've had enough punishment.
or 3.2 if you're a stupid person from indiana
Indiana Pi Bill - Wikipedia, the free encyclopedia
 
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