Taylor Series X3
1. **Problem Statement:** Determine the Taylor series for the function $f(x) = x^3$ at $a=2$.
2. **Taylor Series Formula:** The Taylor series of a function $f(x)$ at $x=a$ is given by:
$$f(x) = \sum_{n=0}^\infty \frac{f^{(n)}(a)}{n!} (x - a)^n$$
where $f^{(n)}(a)$ is the $n$th derivative of $f$ evaluated at $a$.
3. **Calculate derivatives of $f(x) = x^3$:**
- $f(x) = x^3$
- $f'(x) = 3x^2$
- $f''(x) = 6x$
- $f^{(3)}(x) = 6$
- $f^{(n)}(x) = 0$ for $n \geq 4$
4. **Evaluate derivatives at $a=2$:**
- $f(2) = 2^3 = 8$
- $f'(2) = 3 \times 2^2 = 12$
- $f''(2) = 6 \times 2 = 12$
- $f^{(3)}(2) = 6$
5. **Write the Taylor series:**
$$
\begin{aligned}
f(x) &= f(2) + f'(2)(x-2) + \frac{f''(2)}{2!}(x-2)^2 + \frac{f^{(3)}(2)}{3!}(x-2)^3 \\
&= 8 + 12(x-2) + \frac{12}{2}(x-2)^2 + \frac{6}{6}(x-2)^3 \\
&= 8 + 12(x-2) + 6(x-2)^2 + (x-2)^3
\end{aligned}
$$
6. **Explanation:** The Taylor series expresses $f(x)$ as a polynomial centered at $a=2$ using derivatives at that point. Since $f(x) = x^3$ is a polynomial of degree 3, the Taylor series terminates at the third derivative.
**Final answer:**
$$f(x) = 8 + 12(x-2) + 6(x-2)^2 + (x-2)^3$$