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Function \(f(x)\) by Maclaurin’s series (as an infinite series) can be expressed as

  • A.\(f(x)=f(1)+xf'(1)+\frac{x^2}{2!}f''(1)+\frac{x^3}{3!}f'''(1)+\cdots+\infty\)
  • B.\(f(x)=f(0)+xf'(0)+\frac{x^2}{2!}f''(0)+\frac{x^3}{3!}f'''(0)+\cdots+\infty\)
  • C.\(f(x)=f(1)-xf'(1)+\frac{x^2}{2!}f''(1)-\frac{x^3}{3!}f'''(1)+\cdots+\infty\)
  • D.\(f(x)=f(0)-xf'(0)+\frac{x^2}{2!}f''(0)-\frac{x^3}{3!}f'''(0)+\cdots+\infty\)

Answer: B

The Maclaurin series is \(f(x) = f(0) + xf'(0) + \frac{x^{2}}{2!}f''(0) + \frac{x^{3}}{3!}f'''(0) + \cdots\).

Maclaurin’s series is the Taylor series expanded about \(x = 0\). The general Taylor series about a point \(a\) is

\[ f(x) = \sum_{k=0}^{\infty} \frac{f^{(k)}(a)}{k!}(x - a)^{k} \]

and with \(a = 0\) every term has the derivative evaluated at 0 and a power of \(x\), all with plus signs.

The options evaluating derivatives at 1 are not Maclaurin series, and a Taylor series about 1 would need powers of \((x - 1)\), not \(x\). The alternating-sign version at 0 is the series for \(f(-x)\), not \(f(x)\).

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