The Official .9999999999 Appreciation Page

The Official .9999999999 Appreciation Page

by Cliff Pickover, Reality Carnival

I've been in love with the number .99999999 for almost all of my life.

In mathematics, 0.999... is exactly equal to 1. This seems to be so mysterious. In other words, the symbols '0.999...' and '1' represent the same number. Yet, a number of proofs of this identity have been formulated.

A related mystery is "The mystery of 0.33333".
We all know that 1/3 = 0.3333... repeating. Multiplying both sides of the equation by 3, we find that 1 = 0.9999.... How can this be?

Answer from the book A Passion for Mathematics: The reason that we find 1 = 0.9999... is because it is true. There are numerous mathematical ways to show this involving the sum of an infinite series, but my favorite way doesn't involve too much math. Consider that any two distinct (different) real numbers must have another number in between them. However, there is no number between 1 and 0.9999.... Thus, 1 and 0.9999... are not different numbers. (Of course, this question becomes slightly more complicated when considering alternative number systems, including those that consider an "Absolute Continuum.")

Additional web sites devoted to the beauty and wonder of 0.9999999999999999.... include:

  1. .9999 is amazing
  2. I love .9999
  3. .9999 rules the world
999-999-9999 is also the name of a horror movie. A transfer student becomes the center of her attention at her new school when she relates the tales of the mysterious deaths at her old school. She reports that the deaths are linked to an evil phone number - 999-999-999, that will grant the wish of any caller - but with a price. Despite her warnings against using the phone number, many of her new friends cannot resist the temptation and one by one they meet with a grisly 'accident'.

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