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The familiar decimal notation for real numbers can also be viewed as an example of a power series, with integer coefficients, but with the argument x fixed at 1 ⁄ 10. In number theory, the concept of p-adic numbers is also closely related to that of a power series.
Since y is real, that happens only if cos(y) = 1 and sin(y) = 0, so that y is an integer multiple of 2 π. Consequently the singular points of this function occur at z = a nonzero integer multiple of 2 π i. The singularities nearest 0, which is the center of the power series expansion, are at ±2 π i.
The left-hand side is the Maclaurin series expansion of the right-hand side. Alternatively, the equality can be justified by multiplying the power series on the left by 1 − x, and checking that the result is the constant power series 1 (in other words, that all coefficients except the one of x 0 are equal to 0). Moreover, there can be no ...
By definition, a function f : I → R is real analytic if it is locally defined by a convergent power series. This means that for every a ∈ I there exists some r > 0 and a sequence of coefficients c k ∈ R such that ( a − r , a + r ) ⊂ I and
The exponential function (in blue), and the sum of the first n + 1 terms of its power series (in red) where ! is the factorial of n (the product of the n first positive integers). This series is absolutely convergent for every per the ratio test. So, the derivative of the sum can be computed by term-by-term derivation, and this shows that the ...
A Laurent series is a generalization of the Taylor series, allowing terms with negative exponents; it takes the form = and converges in an annulus. [6] In particular, a Laurent series can be used to examine the behavior of a complex function near a singularity by considering the series expansion on an annulus centered at the singularity.
This expansion is a Maclaurin series, so the n th cumulant can be obtained by differentiating the above expansion n times and evaluating the result at zero: [1] = (). If the moment-generating function does not exist, the cumulants can be defined in terms of the relationship between cumulants and moments discussed later.
Formal power series are used in combinatorics to describe and study sequences that are otherwise difficult to handle, for example, using the method of generating functions. The Hilbert–Poincaré series is a formal power series used to study graded algebras.