0.999...

In mathematics, the repeating decimal 0.999... denotes a real number that can be shown to be the number one. In other words, the symbols 0.999... and 1 represent the same number.

The proof is very simple; 1/3 equals to 0.333..., 1/3 x 3 equals to 1, and 0.333... x 3 equals to 0.999..., therefore 0.999... equals to 1.

So amazing equation.