Definition: Taylor Series

Let ff be a function that has derivatives of all orders at x=cx = c (i.e. ff is infinitely differentiable, or smooth, at cc). The Taylor series of ff centered at cc is the power series

∑n=0∞f(n)(c)n!(x−c)n=f(c)+f′(c)(x−c)+f′′(c)2!(x−c)2+f′′′(c)3!(x−c)3+⋯ ,\sum_{n=0}^{\infty} \frac{f^{(n)}(c)}{n!}(x-c)^n = f(c) + f'(c)(x-c) + \frac{f''(c)}{2!}(x-c)^2 + \frac{f'''(c)}{3!}(x-c)^3 + \cdots,

where f(n)(c)f^{(n)}(c) denotes the nn-th derivative of ff evaluated at cc (with f(0)(c)=f(c)f^{(0)}(c) = f(c) and 0!=10! = 1).

The coefficients cn=f(n)(c)/n!c_n = f^{(n)}(c)/n! are called the Taylor coefficients of ff at cc.

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