A graphic illustration of 0.999…=1
plasmasturm.org
plasmasturm.org
x = 0.999999....... (1)
10x = 9.999999....... (2)
Perform (2) minus (1)
9x = 9
x = 1
When I wrote it on the board, I still remember the awe in my friend's faces. And all I was doing was using the standard method to convert a recurring decimal into a fraction. :)
Was Mt. Everest still not the highest mountain even before it was discovered? The need for "seeing is believing", applied to math is pretty childish.
If you're simply not convinced by his line of thought (it's hard to tell...), an alternative argument might be: noting that 3 multiplied by one third is 1, consider what that would look like if written out in decimal notation.
(I am sure there are plenty more arguments too, probably much better than mine.)
and since 1/inf is 0
0.(999) = 1
Check the same reasoning in mathematical notation: http://upload.wikimedia.org/math/6/f/a/6fa510b44742046a167b4...
ahh .5 * 2 = 1
Whereas 0.999... just isn't relatable at all, it's a concept that purely exists for the sake of mathematics.
Not to mention, your examples are all sums, 0.999... = 1 isn't. You can call them all equations, sure, but the difference is that between "if I make changes to X then it can equal Y" and "X already equals Y, even though they appear to be different numbers".
1/9 = .111...
2/9 = .222...
3/9 = .333...
4/9 = .444...
5/9 = .555...
6/9 = .666...
7/9 = .777...
8/9 = .888...
9/9 = .999... = 1
the .999 = 1 issue is not a math problem so much as a symbol issue. Those fractional representations of ninths are presented to 4th graders if i recall correctly, yet adults will argue that there must exist some number between .999... and 1 even though both symbols represent the same value.1 * 10^(-inf)