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In mathematics, the infinite series 1 / 2 + 1 / 4 + 1 / 8 + 1 / 16 + ··· is an elementary example of a geometric series that converges absolutely. The sum of the series is 1. In summation notation, this may be expressed as
The first four partial sums of 1 + 2 + 4 + 8 + ⋯. In mathematics, 1 + 2 + 4 + 8 + ⋯ is the infinite series whose terms are the successive powers of two. As a geometric series, it is characterized by its first term, 1, and its common ratio, 2. As a series of real numbers it diverges to infinity, so the sum of this series is infinity.
[3] The divergence of the harmonic series was first proven in 1350 by Nicole Oresme. [2] [4] Oresme's work, and the contemporaneous work of Richard Swineshead on a different series, marked the first appearance of infinite series other than the geometric series in mathematics. [5] However, this achievement fell into obscurity. [6]
where f (2k−1) is the (2k − 1)th derivative of f and B 2k is the (2k)th Bernoulli number: B 2 = 1 / 6 , B 4 = − + 1 / 30 , and so on. Setting f ( x ) = x , the first derivative of f is 1, and every other term vanishes, so [ 15 ]
Pairing up the terms of the series 1 / 2 − 1 / 4 + 1 / 8 − 1 / 16 + ⋯ results in another geometric series with the same sum, 1 / 4 + 1 / 16 + 1 / 64 + 1 / 256 + ⋯. This series is one of the first to be summed in the history of mathematics; it was used by Archimedes circa ...
a 0 = 1, a 1 = 2, a 2 = 4, a 3 = 8,... The sequence of forward differences is then Δa 0 = a 1 − a 0 = 2 − 1 = 1, Δa 1 = a 2 − a 1 = 4 − 2 = 2, Δa 2 = a 3 − a 2 = 8 − 4 = 4, Δa 3 = a 4 − a 3 = 16 − 8 = 8,... which is just the same sequence. Hence the iterated forward difference sequences all start with Δ n a 0 = 1 for every ...
The idea becomes clearer by considering the general series 1 − 2x + 3x 2 − 4x 3 + 5x 4 − 6x 5 + &c. that arises while expanding the expression 1 ⁄ (1+x) 2, which this series is indeed equal to after we set x = 1.
Unit fractions can also be expressed using negative exponents, as in 2 −1, which represents 1/2, and 2 −2, which represents 1/(2 2) or 1/4. A dyadic fraction is a common fraction in which the denominator is a power of two, e.g. 1 / 8 = 1 / 2 3 . In Unicode, precomposed fraction characters are in the Number Forms block.