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A modest extension of the version of de Moivre's formula given in this article can be used to find the n-th roots of a complex number for a non-zero integer n. (This is equivalent to raising to a power of 1 / n). If z is a complex number, written in polar form as = ( + ),
The 5th roots of unity (blue points) in the complex plane. In mathematics, a root of unity, occasionally called a de Moivre number, is any complex number that yields 1 when raised to some positive integer power n. Roots of unity are used in many branches of mathematics, and are especially important in number theory, the theory of group ...
de Branges's theorem (complex analysis) de Bruijn's theorem (discrete geometry) De Bruijn–Erdős theorem (incidence geometry) De Bruijn–Erdős theorem (graph theory) De Finetti's theorem (probability) De Franchis theorem (Riemann surfaces) De Gua's theorem ; De Moivre's theorem (complex analysis) De Rham's theorem (differential topology)
The cubic root of -1, obtained by De Moivre's formula, is 0.5+0.866i, -1, 0.5-0.866i. I do not see a problem with the formula when n is a rational number. 70.53.228.108 02:38, 21 November 2014 (UTC)Cucaracha The cube root of −1 is also −1 using your logic and De Moivre's formula so all three are the same by your reasoning.
It follows from the present theorem and the fundamental theorem of algebra that if the degree of a real polynomial is odd, it must have at least one real root. [2] This can be proved as follows. Since non-real complex roots come in conjugate pairs, there are an even number of them;
Carathéodory kernel theorem; Carathéodory's theorem (conformal mapping) Carleson–Jacobs theorem; Carlson's theorem; Casorati–Weierstrass theorem; Cauchy–Hadamard theorem; Cauchy's integral formula; Cauchy's integral theorem; Classification of Fatou components; Complex conjugate root theorem; Corona theorem
For simple roots, this results immediately from the implicit function theorem. This is true also for multiple roots, but some care is needed for the proof. A small change of coefficients may induce a dramatic change of the roots, including the change of a real root into a complex root with a rather large imaginary part (see Wilkinson's polynomial).
As in complex analysis of functions of one variable, which is the case n = 1, the functions studied are holomorphic or complex analytic so that, locally, they are power series in the variables z i. Equivalently, they are locally uniform limits of polynomials; or locally square-integrable solutions to the n-dimensional Cauchy–Riemann equations.