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This means that is not a rational number; that is to say, is irrational. This proof was hinted at by Aristotle, in his Analytica Priora, §I.23. [12] It appeared first as a full proof in Euclid's Elements, as proposition 117 of Book X.
Perhaps the numbers most easy to prove irrational are certain logarithms. Here is a proof by contradiction that log 2 3 is irrational (log 2 3 ≈ 1.58 > 0). Assume log 2 3 is rational. For some positive integers m and n, we have =. It follows that / =
Hippasus is sometimes credited with the discovery of the existence of irrational numbers, following which he was drowned at sea. Pythagoreans preached that all numbers could be expressed as the ratio of integers, and the discovery of irrational numbers is said to have shocked them. However, the evidence linking the discovery to Hippasus is unclear.
This same constant can be used to prove that "an irrational elevated to an irrational power may be rational", even without first proving its transcendence. The proof proceeds as follows: either 2 2 {\displaystyle {\sqrt {2}}^{\sqrt {2}}} is a rational which proves the theorem, or it is irrational (as it turns out to be) and then
In 1840, Liouville published a proof of the fact that e 2 is irrational [10] followed by a proof that e 2 is not a root of a second-degree polynomial with rational coefficients. [11] This last fact implies that e 4 is irrational. His proofs are similar to Fourier's proof of the irrationality of e.
Written in 1873, this proof uses the characterization of as the smallest positive number whose half is a zero of the cosine function and it actually proves that is irrational. [ 3 ] [ 4 ] As in many proofs of irrationality, it is a proof by contradiction .
The classic proof that the square root of 2 is irrational is a refutation by contradiction. [11] Indeed, we set out to prove the negation ¬ ∃ a, b ∈ . a/b = √ 2 by assuming that there exist natural numbers a and b whose ratio is the square root of two, and derive a contradiction.
Lemma A also suffices to prove that π is irrational, since otherwise we may write π = k / n, where both k and n are integers) and then ±i π are the roots of n 2 x 2 + k 2 = 0; thus 2 − 1 − 1 = 2e 0 + e i π + e −i π ≠ 0; but this is false.