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  2. List of unsolved problems in mathematics - Wikipedia

    en.wikipedia.org/wiki/List_of_unsolved_problems...

    Many mathematical problems have been stated but not yet solved. These problems come from many areas of mathematics, such as theoretical physics, computer science, algebra, analysis, combinatorics, algebraic, differential, discrete and Euclidean geometries, graph theory, group theory, model theory, number theory, set theory, Ramsey theory, dynamical systems, and partial differential equations.

  3. Collatz conjecture - Wikipedia

    en.wikipedia.org/wiki/Collatz_conjecture

    less than 10 11 is 75 128 138 247, which has 1228 steps, less than 10 12 is 989 345 275 647, which has 1348 steps. [11] (sequence A284668 in the OEIS) These numbers are the lowest ones with the indicated step count, but not necessarily the only ones below the given limit. As an example, 9 780 657 631 has 1132 steps, as does 9 780 657 630.

  4. Lagrange's identity - Wikipedia

    en.wikipedia.org/wiki/Lagrange's_identity

    Lagrange's identity for complex numbers has been obtained from a straightforward product identity. A derivation for the reals is obviously even more succinct. Since the Cauchy–Schwarz inequality is a particular case of Lagrange's identity, [4] this proof is yet another way to obtain the CS inequality. Higher order terms in the series produce ...

  5. Complex number - Wikipedia

    en.wikipedia.org/wiki/Complex_number

    A complex number can be visually represented as a pair of numbers (a, b) forming a vector on a diagram called an Argand diagram, representing the complex plane. Re is the real axis, Im is the imaginary axis, and i is the "imaginary unit", that satisfies i 2 = −1.

  6. List of complex analysis topics - Wikipedia

    en.wikipedia.org/wiki/List_of_complex_analysis...

    Complex analysis, traditionally known as the theory of functions of a complex variable, is the branch of mathematics that investigates functions of complex numbers.It is useful in many branches of mathematics, including number theory and applied mathematics; as well as in physics, including hydrodynamics, thermodynamics, and electrical engineering.

  7. Stark–Heegner theorem - Wikipedia

    en.wikipedia.org/wiki/Stark–Heegner_theorem

    In number theory, the Heegner theorem [1] establishes the complete list of the quadratic imaginary number fields whose rings of integers are principal ideal domains. It solves a special case of Gauss's class number problem of determining the number of imaginary quadratic fields that have a given fixed class number.

  8. cis (mathematics) - Wikipedia

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

    x is the argument of the complex number (angle between line to point and x-axis in polar form). The notation is less commonly used in mathematics than Euler's formula, e ix, which offers an even shorter notation for cos x + i sin x, but cis(x) is widely used as a name for this function in software libraries.

  9. Hurwitz's theorem (composition algebras) - Wikipedia

    en.wikipedia.org/wiki/Hurwitz's_theorem...

    If g in G is not in the center its conjugacy class is exactly g and εg. Thus there are 2 N − 1 + 1 conjugacy classes for N odd and 2 N − 1 + 2 for N even. G has | G / [G, G] | = 2 N − 1 1-dimensional complex representations. The total number of irreducible complex representations is the number of conjugacy classes.