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Answers for “为什么 f(0) 等于 1?”

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The video presents the single-parameter exponential smoothing update rule. The new forecast equals the prior forecast plus a fraction alpha of the prior forecast error, where the error is measured as actual minus forecast from the previous period.

Conditions: Used recursively over discrete time periods.; Requires a starting forecast value.; In the example, alpha is supplied as 0.2.

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The Maclaurin series for the cosine function is the infinite power series cos⁡x=1−x22!+x44!−x66!+…\cos x = 1 - \frac{x^2}{2!} + \frac{x^4}{4!} - \frac{x^6}{6!} + \ldots, which can be written in summation notation as ∑k=0∞(−1)kx2k(2k)!\sum_{k=0}^{\infty}\frac{(-1)^k x^{2k}}{(2k)!}. The video reveals that the specific series-defined function f(x)f(x) is exactly equivalent to cos⁡x\cos x for all real numbers.

Conditions: The variable xx is a real number.; The series is evaluated at x=0x=0 (Maclaurin series).