Thread: .9999...=1
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Old November 27th, 2012, 07:08 PM   #42 (permalink)
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Originally Posted by SUroot View Post
Actually words 7 and 9 of my post take this into account when combined with the rest of the first sentence

If you look how your maths is written, you have .9999 ad infinitum but when you multiply it by 10, you magically have add infinitum + 1 extra digit, which is why your maths looks to work. But we all know .99999 blah is not actually 1.

Since infinity isn't really a number, it can't really be used in maths to form any cohesive proof that 1 isn't 1.

If you massage numbers correctly, you can "prove" anything and you did a good job of massaging them. Well done. But joking aside, .9 reoccurring is nothing except what it is, even if you can make it appear so on paper. Maths is the last bastion of comedy.
You certainly use infinity in math, it's one of the entire foundations of Calculus. The ability to take limits as a variable goes to positive or negative infinity is a subject that comes up in multiple topics such as horizontal asymptotes, anti-derivatives/integrals, improper integrals, and sums of infinite series. For the record, I am a college mathematics professor who teaches these topics in Calculus I & II. I never claimed to be good with taxes, just with mathematical theory. I noticed that people picked apart my algebraic proof with skepticism, but flat out ignored my proof through analysis most likely because very few ever take 4th year mathematics courses when single variable calculus is considered to be first year. As promised, I am going to provide the proof that anyone who has taken calculus II could do by use of the Geometric Series. Just so people don't think I pull formulas out of thin air, I'm actually going to use a formula in this proof that you can look up in any calculus textbook, and I will even cite one, James Stewart's Calculus Early Transcendentals 5th Edition(ISBN:0-534-39321-7). Because the proof requires the use of symbols not easily typed, I have hand written it and attached it to this. Hopefully this will be much more convincing.
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