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  2. Rational root theorem - Wikipedia

    en.wikipedia.org/wiki/Rational_root_theorem

    The theorem is used to find all rational roots of a polynomial, if any. It gives a finite number of possible fractions which can be checked to see if they are roots. If a rational root x = r is found, a linear polynomial ( x – r ) can be factored out of the polynomial using polynomial long division , resulting in a polynomial of lower degree ...

  3. Commensurability (mathematics) - Wikipedia

    en.wikipedia.org/wiki/Commensurability_(mathematics)

    In mathematics, two non-zero real numbers a and b are said to be commensurable if their ratio ⁠ a / b ⁠ is a rational number; otherwise a and b are called incommensurable. (Recall that a rational number is one that is equivalent to the ratio of two integers.) There is a more general notion of commensurability in group theory.

  4. Erdős–Ulam problem - Wikipedia

    en.wikipedia.org/wiki/Erdős–Ulam_problem

    In 1946, Stanislaw Ulam asked whether there exists a set of points at rational distances from each other that forms a dense subset of the Euclidean plane. [2] While the answer to this question is still open, József Solymosi and Frank de Zeeuw showed that the only irreducible algebraic curves that contain infinitely many points at rational distances are lines and circles. [3]

  5. Irrationality measure - Wikipedia

    en.wikipedia.org/wiki/Irrationality_measure

    In mathematics, an irrationality measure of a real number is a measure of how "closely" it can be approximated by rationals. If a function f ( t , λ ) {\displaystyle f(t,\lambda )} , defined for t , λ > 0 {\displaystyle t,\lambda >0} , takes positive real values and is strictly decreasing in both variables, consider the following inequality :

  6. Rational variety - Wikipedia

    en.wikipedia.org/wiki/Rational_variety

    Any rational variety is thus, by definition, stably rational. Examples constructed by Beauville et al. (1985) show, that the converse is false however. Schreieder (2019) showed that very general hypersurfaces V ⊂ P N + 1 {\displaystyle V\subset \mathbf {P} ^{N+1}} are not stably rational, provided that the degree of V is at least log 2 ⁡ N ...

  7. Niven's theorem - Wikipedia

    en.wikipedia.org/wiki/Niven's_theorem

    The theorem extends to the other trigonometric functions as well. [2] For rational values of θ, the only rational values of the sine or cosine are 0, ±1/2, and ±1; the only rational values of the secant or cosecant are ±1 and ±2; and the only rational values of the tangent or cotangent are 0 and ±1. [3]

  8. Rational point - Wikipedia

    en.wikipedia.org/wiki/Rational_point

    In number theory and algebraic geometry, a rational point of an algebraic variety is a point whose coordinates belong to a given field. If the field is not mentioned, the field of rational numbers is generally understood. If the field is the field of real numbers, a rational point is more commonly called a real point.

  9. Rational number - Wikipedia

    en.wikipedia.org/wiki/Rational_number

    In mathematics, "rational" is often used as a noun abbreviating "rational number". The adjective rational sometimes means that the coefficients are rational numbers. For example, a rational point is a point with rational coordinates (i.e., a point whose coordinates are rational numbers); a rational matrix is a matrix of rational numbers; a rational polynomial may be a polynomial with rational ...