Section 5.5 Summary
Subsection 5.5.1 Common Maclaurin Series
\begin{align*}
\boxed{
\begin{aligned}
\frac{1}{1-x} \amp= \sum_{n=0}^{\infty} x^{n}
\amp= 1 + x + x^{2} + x^{3} + \cdots
\amp\quad -1 < x < 1
\\[0.6ex]
e^{x} \amp= \sum_{n=0}^{\infty} \frac{x^{n}}{n!}
\amp= 1 + x + \frac{x^{2}}{2!} + \frac{x^{3}}{3!} + \cdots
\amp\quad -\infty < x < \infty
\\[0.6ex]
\sin x \amp= \sum_{n=0}^{\infty} (-1)^{n}\frac{x^{2n+1}}{(2n+1)!}
\amp= x - \frac{x^{3}}{3!} + \frac{x^{5}}{5!} - \frac{x^{7}}{7!} + \cdots
\amp\quad -\infty < x < \infty
\\[0.6ex]
\cos x \amp= \sum_{n=0}^{\infty} (-1)^{n}\frac{x^{2n}}{(2n)!}
\amp= 1 - \frac{x^{2}}{2!} + \frac{x^{4}}{4!} - \frac{x^{6}}{6!} + \cdots
\amp\quad -\infty < x < \infty
\\[0.6ex]
\ln(1+x) \amp= \sum_{n=0}^{\infty} (-1)^n \frac{x^{n+1}}{n+1}
\amp= x - \frac{x^{2}}{2} + \frac{x^{3}}{3} - \frac{x^{4}}{4} + \cdots
\amp\quad -1 < x \le 1
\\[0.6ex]
\arctan x \amp= \sum_{n=0}^{\infty} (-1)^{n}\frac{x^{2n+1}}{2n+1}
\amp= x - \frac{x^{3}}{3} + \frac{x^{5}}{5} - \frac{x^{7}}{7} + \cdots
\amp\quad -1 \le x \le 1
\end{aligned}}
\end{align*}
Subsection 5.5.2 Key Skills
-
Find interval of convergence and radius of convergence of a power series.
-
Find power series representation of a function, and determine interval of convergence.
-
Evaluate a limit, using series.
-
Find an antiderivative of a function as a power series, using series.
-
Approximate an integral, with some accuracy, using series.
Subsection 5.5.3 More Maclaurin Series
\begin{align*}
\tan x \amp = x + \frac{x^3}{3} + \frac{2x^5}{15} + \frac{17x^7}{315} + \cdots, \quad \lvert x\rvert < \frac{\pi}{2} \\\\
(1+x)^n \amp = 1 + nx + \frac{n(n-1)}{2!}x^2 + \frac{n(n-1)(n-2)}{3!}x^3 + \cdots
= \sum_{k=0}^{\infty} \binom{n}{k} x^k, \quad \lvert x\rvert < 1 \\\\
\sinh x \amp = x + \frac{x^3}{3!} + \frac{x^5}{5!} + \cdots
= \sum_{n=0}^{\infty} \frac{x^{2n+1}}{(2n+1)!}, \quad -\infty < x < \infty \\\\
\cosh x \amp = 1 + \frac{x^2}{2!} + \frac{x^4}{4!} + \cdots
= \sum_{n=0}^{\infty} \frac{x^{2n}}{(2n)!}, \quad -\infty < x < \infty
\end{align*}
