Taylor Series Quiz with Answers (Polynomials, ROC, Error)

Question 1

Find the Maclaurin series of $\ln(1+x)$ (as a power series).

Accepted Answer

$\displaystyle \sum_{n=0}^{\infty} (-1)^n \frac{x^{n+1}}{n+1}$

Answer

$\displaystyle \sum_{n=0}^{\infty} (-1)^n \frac{x^n}{n+1}$

Answer

$\displaystyle \sum_{n=1}^{\infty} \frac{x^n}{n}$

Answer

$\displaystyle \sum_{n=1}^{\infty} (-1)^{n+1} \frac{x^{n-1}}{n}$

Question 2

Find the Maclaurin series for $\arctan x$.

Accepted Answer

$\displaystyle \sum_{n=0}^{\infty} (-1)^n \frac{x^{2n+1}}{2n+1}$

Answer

$\displaystyle \sum_{n=1}^{\infty} (-1)^n \frac{x^{2n+1}}{2n+1}$

Answer

$\displaystyle \sum_{n=0}^{\infty} (-1)^n \frac{x^{2n}}{2n+1}$

Answer

$\displaystyle \sum_{n=0}^{\infty} \frac{x^{2n+1}}{2n+1}$

Question 3

Use Taylor's theorem to bound the error when approximating $\ln(1.2)$ by the 3rd-degree Maclaurin polynomial of $\ln(1+x)$ (i.e., at $x=0.2$).

Accepted Answer

$\displaystyle |R_3(0.2)| \le \frac{6(0.2)^4}{4!}$

Answer

$\displaystyle |R_3(0.2)| \le \frac{(0.2)^4}{4}$

Answer

$\displaystyle |R_3(0.2)| \le \frac{(0.2)^3}{3!}$

Answer

$\displaystyle |R_3(0.2)| \le \frac{6(0.2)^4}{3!}$

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