Note: This item is an example of a special case - Known Unknowables
An irrational number is a real number that cannot be expressed as a ratio of integers, i.e. as a fraction. Put another way, it can never be specified with absolute accuracy.
Examples are π and √2 (etc.) For many irrational numbers, relatively simple mathematical proofs exist which show that it's impossible to ever arrive at a finite solution.
( √2 was proved to be an irrational number by Greek mathematicians more than 2000 years ago).
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