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  2. Square root of 2 - Wikipedia

    en.wikipedia.org/wiki/Square_root_of_2

    Technically, it should be called the principal square root of 2, to distinguish it from the negative number with the same property. Geometrically, the square root of 2 is the length of a diagonal across a square with sides of one unit of length; this follows from the Pythagorean theorem. It was probably the first number known to be irrational. [1]

  3. Irrational number - Wikipedia

    en.wikipedia.org/wiki/Irrational_number

    The square root of 2 was likely the first number proved irrational. [27] The golden ratio is another famous quadratic irrational number. The square roots of all natural numbers that are not perfect squares are irrational and a proof may be found in quadratic irrationals.

  4. Proof of impossibility - Wikipedia

    en.wikipedia.org/wiki/Proof_of_impossibility

    A more general proof shows that the mth root of an integer N is irrational, unless N is the mth power of an integer n. [7] That is, it is impossible to express the mth root of an integer N as the ratio a ⁄ b of two integers a and b, that share no common prime factor, except in cases in which b = 1.

  5. Proof by infinite descent - Wikipedia

    en.wikipedia.org/wiki/Proof_by_infinite_descent

    In mathematics, a proof by infinite descent, also known as Fermat's method of descent, is a particular kind of proof by contradiction [1] used to show that a statement cannot possibly hold for any number, by showing that if the statement were to hold for a number, then the same would be true for a smaller number, leading to an infinite descent and ultimately a contradiction. [2]

  6. Algebraic expression - Wikipedia

    en.wikipedia.org/wiki/Algebraic_expression

    Since taking the square root is the same as raising to the power ⁠ 1 / 2 ⁠, the following is also an algebraic expression: 1 − x 2 1 + x 2 {\displaystyle {\sqrt {\frac {1-x^{2}}{1+x^{2}}}}} An algebraic equation is an equation involving polynomials , for which algebraic expressions may be solutions .

  7. Irrationality measure - Wikipedia

    en.wikipedia.org/wiki/Irrationality_measure

    Rational numbers have irrationality exponent 1, while (as a consequence of Dirichlet's approximation theorem) every irrational number has irrationality exponent at least 2. On the other hand, an application of Borel-Cantelli lemma shows that almost all numbers, including all algebraic irrational numbers , have an irrationality exponent exactly ...

  8. Constructive proof - Wikipedia

    en.wikipedia.org/wiki/Constructive_proof

    The square root of 2 is irrational, and 3 is rational. ⁡ is also irrational: if it were equal to , then, by the properties of logarithms, 9 n would be equal to 2 m, but the former is odd, and the latter is even. A more substantial example is the graph minor theorem.

  9. Algebraic number - Wikipedia

    en.wikipedia.org/wiki/Algebraic_number

    The square root of 2 is an algebraic number equal to the length of the hypotenuse of a right triangle with legs of length 1.. An algebraic number is a number that is a root of a non-zero polynomial in one variable with integer (or, equivalently, rational) coefficients.