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  2. 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.

  3. 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.

  4. Rational variety - Wikipedia

    en.wikipedia.org/wiki/Rational_variety

    This definition differs from that of path connectedness only by the nature of the path, but is very different, as the only algebraic curves which are rationally connected are the rational ones. Every rational variety, including the projective spaces, is rationally connected, but the converse is false. The class of the rationally connected ...

  5. Glossary of algebraic geometry - Wikipedia

    en.wikipedia.org/wiki/Glossary_of_algebraic_geometry

    There is a bijection between the set of k-rational points of |D| and the set of effective Weil divisors on X that are linearly equivalent to D. [1] The same definition is used if D is a Cartier divisor on a complete variety over k. [X/G] The quotient stack of, say, an algebraic space X by an action of a group scheme G. / /

  6. 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 ...

  7. Arithmetic geometry - Wikipedia

    en.wikipedia.org/wiki/Arithmetic_geometry

    The hyperelliptic curve defined by = (+) (+) has only finitely many rational points (such as the points (,) and (,)) by Faltings's theorem.. In mathematics, arithmetic geometry is roughly the application of techniques from algebraic geometry to problems in number theory. [1]

  8. Glossary of mathematical symbols - Wikipedia

    en.wikipedia.org/wiki/Glossary_of_mathematical...

    A mathematical symbol is a figure or a combination of figures that is used to represent a mathematical object, an action on mathematical objects, a relation between mathematical objects, or for structuring the other symbols that occur in a formula. As formulas are entirely constituted with symbols of various types, many symbols are needed for ...

  9. 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]