Root 2

The square root of 2 is sometime's called Pythagoras's constant since he was the first to prove that the number is irrational.

√2 when multiplied by itself, gives the number 2.

√2

1.414213562373095048801688724209698 (and more ...)

also know as root 2 or radical 2, The "Principal square root of 2" is to distinguish it from the negative number with the same property.

The square root of 2 is equal to the length of the hypotenuse of a right triangle with legs of length 1.

one very practical use of √2 is in a range of paper sizes used in Britain and Europe called A0, A1, A2, etc. A4 is the size used for large sheets of writing paper, for files, etc. A0 is a square metre in area. A1 is A0 folded in half (and turned the other way up). A2 is A1 folded in half, and so on. All sheets are the same shape. This will only work if they all have their sides in proportion 1 to √2.