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| − | + | ==개요== | |
0.9999… = 1 이다. | 0.9999… = 1 이다. | ||
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| − | + | ==메모== | |
| − | + | * http://sprott.physics.wisc.edu/pickover/pc/9999.html | |
| − | |||
| − | |||
| − | + | ==노트== | |
| + | ===말뭉치=== | ||
| + | # One might argue that when multiplying by ten, the right hand side shifts to the left a decimal place, leaving a terminating zero at the end of the infinite string of 9's ( ).<ref name="ref_81c60dff">[https://math.wikia.org/wiki/Proof:The_Decimal_0.999..._is_Equivalent_to_1 Proof:The Decimal 0.999... is Equivalent to 1]</ref> | ||
| + | # And, therefore, when subtracting (with a one after the last of infinite nines).<ref name="ref_81c60dff" /> | ||
| + | # It is impossible to find a "next higher" number that is both larger to a given value but couldnt have been smaller (see argument from averages).<ref name="ref_81c60dff" /> | ||
| + | # One might argue that after the infinitely many zeros, there is going to be a 1 ( ).<ref name="ref_81c60dff" /> | ||
| + | # The sequence S = (0.9, 0.99, 0.999, … ) is bounded above by 1.0, so the least upper bound is not greater than 1.0.<ref name="ref_daa472c2">[https://thatsmaths.com/2019/01/10/really-0-999999-is-equal-to-1-surreally-this-is-not-so/ Really, 0.999999… is equal to 1. Surreally, this is not so!]</ref> | ||
| + | # If we consider the surreal number 0.999… (see earlier post), we may assume that there are ω 9s after the decimal.<ref name="ref_daa472c2" /> | ||
| + | # Return to the Lessons Index | Do the Lessons in Order | Print-friendly page How Can 0.999... = 1?<ref name="ref_d594d900">[https://www.purplemath.com/modules/howcan1.htm How Can 0.999... = 1?]</ref> | ||
| + | # Whatever the reason, many students (me included) have, at one time or another, felt uncomfortable with this equality.<ref name="ref_d594d900" /> | ||
| + | # The ellipsis (the "dot, dot, dot" after the last 9 ) means "goes on forever in like manner".<ref name="ref_d594d900" /> | ||
| + | # Yes, at any given stop, at any given stage of the expansion, for any given finite number of 9 s, there will be a difference between 0.999...9 and 1 .<ref name="ref_d594d900" /> | ||
| + | # In mathematics, 0.999... (also written as 0.9, in repeating decimal notation) denotes the repeating decimal consisting of infinitely many 9s after the decimal point.<ref name="ref_acb2a2a7">[https://en.wikipedia.org/wiki/0.999... Wikipedia]</ref> | ||
| + | # In other words, "0.999..." and "1" represent the same number.<ref name="ref_acb2a2a7" /> | ||
| + | # The technique used depends on the target audience, background assumptions, historical context, and preferred development of the real numbers, the system within which 0.999... is commonly defined.<ref name="ref_acb2a2a7" /> | ||
| + | # More generally, every nonzero terminating decimal has two equal representations (for example, 8.32 and 8.31999...), which is a property of all base representations.<ref name="ref_acb2a2a7" /> | ||
| + | # So when we learn math in elementary school we are told: Every real number can be written as a decimal expansion (maybe infinite) and every possible decimal expansion is a real number.<ref name="ref_48c663f0">[https://math.stackexchange.com/questions/11/is-it-true-that-0-999999999-dots-1 Is it true that $0.999999999\dots=1$?]</ref> | ||
| + | # we take it on faith that: Every real number can be written as a decimal expansion (maybe infinite) and every possible decimal expansion is a real number.<ref name="ref_48c663f0" /> | ||
| + | # (So it can be all the elements less than 1/2 but it can't be all the elements less than or equal to 1/2).<ref name="ref_48c663f0" /> | ||
| + | # Notice sometimes the cut will occur at a rational number (all the rationals less than 1/2), but sometimes it will occur at points "between" the rational numbers.<ref name="ref_48c663f0" /> | ||
| + | # 다행히도, 임의의 무한소수에 대해 수열의 극한값은 존재하고, 그 극한값은 이 수열의 상한(supremum), 풀어 쓰면 '모든 자연수에 대해보다 크거나 같은 숫자의 집합에서 가장 작은 수' 와 같다.이를 증명하기는 어렵지 않다.<ref name="ref_36083143">[https://namu.wiki/w/0.999%E2%80%A6%3D1 0.999…=1]</ref> | ||
| + | # IF the two numbers 0.99999... and 1 were NOT equal, you would have a number to represent the difference (the GAP or Distance between them) - and it should not be 0.<ref name="ref_36a36aab">[http://mathcentral.uregina.ca/QQ/database/QQ.09.01/catherine1.html 0.999999=1?]</ref> | ||
| + | # Of course it is a bit obscure since we are dealing with 'infinite processes' (sometimes called limits) whenever we work with decimal numbers which do no terminate.<ref name="ref_36a36aab" /> | ||
| + | # If you stop the expansion of 9s at any finite point, the fraction you have (like .99999 = 99999/100000) is never equal to 1.<ref name="ref_cfd5cdc1">[https://www.relativelyinteresting.com/does-0-99999-really-equal-1/ Does 0.99999… really equal 1?]</ref> | ||
| + | # But each time you add a 9, the margin error is smaller (with each 9, the error is actually ten times smaller).<ref name="ref_cfd5cdc1" /> | ||
| + | # You can show (using calculus or other summations) that with a large enough number of 9s in the expansion, you can get arbitrarily close to 1.<ref name="ref_cfd5cdc1" /> | ||
| + | # To prove it to yourself that 0.9999… = 1, consider that if they weren’t equal, there would be a number E that is greater than zero such that E = (1 — 0.9999…).<ref name="ref_b8db7dcd">[https://www.tcg.com/blog/why-099999-1-proof-and-limits/ Why 0.99999… = 1, proof, and limits]</ref> | ||
| + | # Since we’re playing this game, you counter and make E smaller, say 10^(-10), and I turn around and say “make D = 11” (because 1 — 0.99999999999 < 10^(-10) ).<ref name="ref_b8db7dcd" /> | ||
| + | # Specifically, if E > 10^(-X) for some positive integer X, then setting D = X will do it.<ref name="ref_b8db7dcd" /> | ||
| + | # There is no E that is greater than zero such that E = (1 — 0.9999…).<ref name="ref_b8db7dcd" /> | ||
| + | # Well, it’s “true” in the same way numbers must be there (positive) or not there (zero) — it’s true because we’ve implicitly excluded other possibilities.<ref name="ref_e1d14936">[https://betterexplained.com/articles/a-friendly-chat-about-whether-0-999-1/ A Friendly Chat About Whether 0.999… = 1 – BetterExplained]</ref> | ||
| + | # The idea behind limits is to find some point at which “a – b” becomes zero (less than any number); that is, we can’t tell the “number to test” and our “result” as different.<ref name="ref_e1d14936" /> | ||
| + | # It’s still tough to compare items when they take such different forms (like an infinite series).<ref name="ref_e1d14936" /> | ||
| + | # Then if you ask for 1, and I give you 0.99, the difference is 0.01 (one hundredth) and you don’t know you’ve been tricked!<ref name="ref_e1d14936" /> | ||
| + | # Student: Are you (looks at Vadim) saying that you (looks at Teacher) made up the definition of a limit just in order to make 0.999…=1?<ref name="ref_8fbbe88f">[https://blogs.helsinki.fi/kulikov/2011/07/04/0-999/ 0.999999….. = 1?]</ref> | ||
| + | # But by the least upper bound axiom of real numbers, if a set of real numbers has a upper bound, then it has a least upper bound (that is a real number).<ref name="ref_7912a8ac">[https://artofproblemsolving.com/wiki/index.php/0.999... Art of Problem Solving]</ref> | ||
| + | # That must mean that one-third of it ("point 3 repeating") is also irrational.<ref name="ref_c122e3b9">[https://www.hltv.org/forums/threads/2070372/09999-1 Forum thread: 0.9999... = 1]</ref> | ||
| + | # And whenever you have an infinite number of parts of something (an infinite number of places in a number, in this case) you might well expect something amazing to happen.<ref name="ref_e8240b85">[https://www.uhigh.ilstu.edu/math/thompson/.999999%20repeating1.htm Ask Dr. Math]</ref> | ||
| + | # Said another way, if your number x = 0.999999999... is such that the difference "x-1" is smaller than any positive number (however small), then we consider x - 1 = 0, so that x = 1.<ref name="ref_e8240b85" /> | ||
| + | # If we do this, we'll get a 9.999990 (slide the decimal in the 0.999999 right 1 places, you'll get 9.999990).<ref name="ref_718b3275">[http://www.webmath.com/cgi-bin/fraction.cgi?decimal=.999999&op=to_fraction&back=dec2fract.html Webmath.com: Doing math with fractions]</ref> | ||
| + | # If you can warranted that you always do the best on your job level, your boss will automatically think that you must get (absolutely get) new level on your job.<ref name="ref_6495662e">[https://brilliant.org/discussions/thread/explain-why-0999-1/ Explain why 0.999... = 1 ?]</ref> | ||
| + | # The standard algebra proof (which, if you modify it a little, works to convert any repeating decimal into a fraction) runs something like this.<ref name="ref_a97b282a">[https://polymathematics.typepad.com/polymath/2006/06/no_im_sorry_it_.html Polymathematics: No, I'm Sorry, It Does.]</ref> | ||
| + | # Those are my first two demonstrations that our fact is true (the last one is at the end).<ref name="ref_a97b282a" /> | ||
| + | # The word "geometric" means that each term of the series is the identical multiple (in this case 1/10) of the previous term.<ref name="ref_a97b282a" /> | ||
| + | # You’ll see the same kind of thing in all languages that support your hardware’s floating-point arithmetic (although some languages may not display the difference by default, or in all output modes).<ref name="ref_a8b68441">[https://python.readthedocs.io/en/v2.7.2/tutorial/floatingpoint.html 14. Floating Point Arithmetic: Issues and Limitations — Python 2.7.2 documentation]</ref> | ||
| + | # The documentation for the built-in round() function says that it rounds to the nearest value, rounding ties away from zero.<ref name="ref_a8b68441" /> | ||
| + | # Since the decimal fraction 2.675 is exactly halfway between 2.67 and 2.68, you might expect the result here to be (a binary approximation to) 2.68.<ref name="ref_a8b68441" /> | ||
| + | # For fine control over how a float is displayed see the str.format() method’s format specifiers in Format String Syntax.<ref name="ref_a8b68441" /> | ||
| + | # If you had a hat with an infinite amount of slips of paper consisting of an infinite amount of numbers, the probability of pulling any random number is zero (1/infinity = 0).<ref name="ref_1579dacc">[https://www.neogaf.com/threads/0-9999-1-true-or-false-and-why.385028/ 0.9999 = 1, true or false and why?]</ref> | ||
| + | # In fact, the probability of pulling any real subset of numbers is zero (i.e. 10000/infinity = 0).<ref name="ref_1579dacc" /> | ||
| − | + | ===소스=== | |
| + | <references /> | ||
| − | + | ==많이 나오는 질문과 답변== | |
| − | + | 많이 나오는 질문과 답변이 아래 링크에 정리되어 있다. | |
| − | + | * http://gall.dcinside.com/list.php?id=mathematics&no=28665&page=1&bbs= | |
| − | + | ** 디씨인사이드 수학 갤러리, [http://gallog.dcinside.com/tmxkskgkwk ε-δ]작성 | |
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2021년 2월 12일 (금) 08:55 기준 최신판
개요
0.9999… = 1 이다.
메모
노트
말뭉치
- One might argue that when multiplying by ten, the right hand side shifts to the left a decimal place, leaving a terminating zero at the end of the infinite string of 9's ( ).[1]
- And, therefore, when subtracting (with a one after the last of infinite nines).[1]
- It is impossible to find a "next higher" number that is both larger to a given value but couldnt have been smaller (see argument from averages).[1]
- One might argue that after the infinitely many zeros, there is going to be a 1 ( ).[1]
- The sequence S = (0.9, 0.99, 0.999, … ) is bounded above by 1.0, so the least upper bound is not greater than 1.0.[2]
- If we consider the surreal number 0.999… (see earlier post), we may assume that there are ω 9s after the decimal.[2]
- Return to the Lessons Index | Do the Lessons in Order | Print-friendly page How Can 0.999... = 1?[3]
- Whatever the reason, many students (me included) have, at one time or another, felt uncomfortable with this equality.[3]
- The ellipsis (the "dot, dot, dot" after the last 9 ) means "goes on forever in like manner".[3]
- Yes, at any given stop, at any given stage of the expansion, for any given finite number of 9 s, there will be a difference between 0.999...9 and 1 .[3]
- In mathematics, 0.999... (also written as 0.9, in repeating decimal notation) denotes the repeating decimal consisting of infinitely many 9s after the decimal point.[4]
- In other words, "0.999..." and "1" represent the same number.[4]
- The technique used depends on the target audience, background assumptions, historical context, and preferred development of the real numbers, the system within which 0.999... is commonly defined.[4]
- More generally, every nonzero terminating decimal has two equal representations (for example, 8.32 and 8.31999...), which is a property of all base representations.[4]
- So when we learn math in elementary school we are told: Every real number can be written as a decimal expansion (maybe infinite) and every possible decimal expansion is a real number.[5]
- we take it on faith that: Every real number can be written as a decimal expansion (maybe infinite) and every possible decimal expansion is a real number.[5]
- (So it can be all the elements less than 1/2 but it can't be all the elements less than or equal to 1/2).[5]
- Notice sometimes the cut will occur at a rational number (all the rationals less than 1/2), but sometimes it will occur at points "between" the rational numbers.[5]
- 다행히도, 임의의 무한소수에 대해 수열의 극한값은 존재하고, 그 극한값은 이 수열의 상한(supremum), 풀어 쓰면 '모든 자연수에 대해보다 크거나 같은 숫자의 집합에서 가장 작은 수' 와 같다.이를 증명하기는 어렵지 않다.[6]
- IF the two numbers 0.99999... and 1 were NOT equal, you would have a number to represent the difference (the GAP or Distance between them) - and it should not be 0.[7]
- Of course it is a bit obscure since we are dealing with 'infinite processes' (sometimes called limits) whenever we work with decimal numbers which do no terminate.[7]
- If you stop the expansion of 9s at any finite point, the fraction you have (like .99999 = 99999/100000) is never equal to 1.[8]
- But each time you add a 9, the margin error is smaller (with each 9, the error is actually ten times smaller).[8]
- You can show (using calculus or other summations) that with a large enough number of 9s in the expansion, you can get arbitrarily close to 1.[8]
- To prove it to yourself that 0.9999… = 1, consider that if they weren’t equal, there would be a number E that is greater than zero such that E = (1 — 0.9999…).[9]
- Since we’re playing this game, you counter and make E smaller, say 10^(-10), and I turn around and say “make D = 11” (because 1 — 0.99999999999 < 10^(-10) ).[9]
- Specifically, if E > 10^(-X) for some positive integer X, then setting D = X will do it.[9]
- There is no E that is greater than zero such that E = (1 — 0.9999…).[9]
- Well, it’s “true” in the same way numbers must be there (positive) or not there (zero) — it’s true because we’ve implicitly excluded other possibilities.[10]
- The idea behind limits is to find some point at which “a – b” becomes zero (less than any number); that is, we can’t tell the “number to test” and our “result” as different.[10]
- It’s still tough to compare items when they take such different forms (like an infinite series).[10]
- Then if you ask for 1, and I give you 0.99, the difference is 0.01 (one hundredth) and you don’t know you’ve been tricked![10]
- Student: Are you (looks at Vadim) saying that you (looks at Teacher) made up the definition of a limit just in order to make 0.999…=1?[11]
- But by the least upper bound axiom of real numbers, if a set of real numbers has a upper bound, then it has a least upper bound (that is a real number).[12]
- That must mean that one-third of it ("point 3 repeating") is also irrational.[13]
- And whenever you have an infinite number of parts of something (an infinite number of places in a number, in this case) you might well expect something amazing to happen.[14]
- Said another way, if your number x = 0.999999999... is such that the difference "x-1" is smaller than any positive number (however small), then we consider x - 1 = 0, so that x = 1.[14]
- If we do this, we'll get a 9.999990 (slide the decimal in the 0.999999 right 1 places, you'll get 9.999990).[15]
- If you can warranted that you always do the best on your job level, your boss will automatically think that you must get (absolutely get) new level on your job.[16]
- The standard algebra proof (which, if you modify it a little, works to convert any repeating decimal into a fraction) runs something like this.[17]
- Those are my first two demonstrations that our fact is true (the last one is at the end).[17]
- The word "geometric" means that each term of the series is the identical multiple (in this case 1/10) of the previous term.[17]
- You’ll see the same kind of thing in all languages that support your hardware’s floating-point arithmetic (although some languages may not display the difference by default, or in all output modes).[18]
- The documentation for the built-in round() function says that it rounds to the nearest value, rounding ties away from zero.[18]
- Since the decimal fraction 2.675 is exactly halfway between 2.67 and 2.68, you might expect the result here to be (a binary approximation to) 2.68.[18]
- For fine control over how a float is displayed see the str.format() method’s format specifiers in Format String Syntax.[18]
- If you had a hat with an infinite amount of slips of paper consisting of an infinite amount of numbers, the probability of pulling any random number is zero (1/infinity = 0).[19]
- In fact, the probability of pulling any real subset of numbers is zero (i.e. 10000/infinity = 0).[19]
소스
- ↑ 1.0 1.1 1.2 1.3 Proof:The Decimal 0.999... is Equivalent to 1
- ↑ 2.0 2.1 Really, 0.999999… is equal to 1. Surreally, this is not so!
- ↑ 3.0 3.1 3.2 3.3 How Can 0.999... = 1?
- ↑ 4.0 4.1 4.2 4.3 Wikipedia
- ↑ 5.0 5.1 5.2 5.3 Is it true that $0.999999999\dots=1$?
- ↑ 0.999…=1
- ↑ 7.0 7.1 0.999999=1?
- ↑ 8.0 8.1 8.2 Does 0.99999… really equal 1?
- ↑ 9.0 9.1 9.2 9.3 Why 0.99999… = 1, proof, and limits
- ↑ 10.0 10.1 10.2 10.3 A Friendly Chat About Whether 0.999… = 1 – BetterExplained
- ↑ 0.999999….. = 1?
- ↑ Art of Problem Solving
- ↑ Forum thread: 0.9999... = 1
- ↑ 14.0 14.1 Ask Dr. Math
- ↑ Webmath.com: Doing math with fractions
- ↑ Explain why 0.999... = 1 ?
- ↑ 17.0 17.1 17.2 Polymathematics: No, I'm Sorry, It Does.
- ↑ 18.0 18.1 18.2 18.3 14. Floating Point Arithmetic: Issues and Limitations — Python 2.7.2 documentation
- ↑ 19.0 19.1 0.9999 = 1, true or false and why?
많이 나오는 질문과 답변
많이 나오는 질문과 답변이 아래 링크에 정리되어 있다.
- http://gall.dcinside.com/list.php?id=mathematics&no=28665&page=1&bbs=
- 디씨인사이드 수학 갤러리, ε-δ작성