Oldest irrational number

According to Official Guinness Records,

The first irrational number discovered was the square root of 2, by Hippasus of Metapontum (then part of Magna Graecia, southern Italy) around 500 BC.
A student of the great mathematician Pythagoras, Hippasus proved that 'root two' could never be expressed as a fraction. Little is known about the secretive Pythagoras and his students, but history suggests that Pythagoras was so enraged by this threat to his concept of perfection in numbers that he ordered Hippasus to be executed by drowning. Only after Pythagoras' death could the study of these new numbers, the irrationals, continue.

For a complete list of Unknown date records, please visit Unknown date Guinness Records in Italy.

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