Taylor Maclaurin
1. Let's start by stating the problem: We want to understand Taylor and Maclaurin series and how to analyze the pattern of derivatives $f^{(n)}(x)$ to find a general formula for the series.
2. The Taylor series of a function $f(x)$ centered at $a$ is given by the formula:
$$f(x) = \sum_{n=0}^\infty \frac{f^{(n)}(a)}{n!}(x - a)^n$$
where $f^{(n)}(a)$ is the $n$th derivative of $f$ evaluated at $x=a$, and $n!$ is the factorial of $n$.
3. The Maclaurin series is a special case of the Taylor series centered at $a=0$:
$$f(x) = \sum_{n=0}^\infty \frac{f^{(n)}(0)}{n!} x^n$$
4. To find the general term of the series, we need to analyze the pattern of the derivatives $f^{(n)}(x)$:
- Compute the first few derivatives $f'(x), f''(x), f^{(3)}(x), \ldots$
- Evaluate each derivative at the center point $a$ (or 0 for Maclaurin).
- Look for a pattern or formula that expresses $f^{(n)}(a)$ in terms of $n$.
5. Once the pattern is identified, substitute it back into the series formula to get the general term:
$$\text{General term} = \frac{f^{(n)}(a)}{n!} (x - a)^n$$
6. Example: For $f(x) = e^x$, all derivatives are $f^{(n)}(x) = e^x$, so $f^{(n)}(0) = 1$. The Maclaurin series is:
$$e^x = \sum_{n=0}^\infty \frac{x^n}{n!}$$
7. Important rules:
- Factorials grow very fast, so terms often get smaller quickly.
- The radius of convergence depends on the function.
- Recognizing the pattern in derivatives is key to writing the series.
In summary, analyzing $f^{(n)}(a)$ means computing derivatives, evaluating at $a$, and finding a formula for the $n$th derivative to write the series compactly.