Derivative Power
1. **Problem Statement:** Prove that the derivative of $x^n$ with respect to $x$ is $nx^{n-1}$.
2. **Formula Used:** The derivative of a function $f(x)$ is defined as
$$f'(x) = \lim_{h \to 0} \frac{f(x+h) - f(x)}{h}$$
3. **Apply the definition to $f(x) = x^n$:**
$$\frac{d}{dx} x^n = \lim_{h \to 0} \frac{(x+h)^n - x^n}{h}$$
4. **Expand $(x+h)^n$ using the Binomial Theorem:**
$$(x+h)^n = \sum_{k=0}^n \binom{n}{k} x^{n-k} h^k = x^n + nx^{n-1}h + \binom{n}{2} x^{n-2} h^2 + \cdots + h^n$$
5. **Substitute the expansion back:**
$$\frac{(x+h)^n - x^n}{h} = \frac{x^n + nx^{n-1}h + \binom{n}{2} x^{n-2} h^2 + \cdots + h^n - x^n}{h}$$
6. **Simplify numerator:**
$$= \frac{nx^{n-1}h + \binom{n}{2} x^{n-2} h^2 + \cdots + h^n}{h}$$
7. **Divide each term by $h$:**
$$= nx^{n-1} + \binom{n}{2} x^{n-2} h + \cdots + h^{n-1}$$
8. **Take the limit as $h \to 0$:**
All terms with $h$ vanish, leaving
$$\lim_{h \to 0} \left(nx^{n-1} + \binom{n}{2} x^{n-2} h + \cdots + h^{n-1}\right) = nx^{n-1}$$
9. **Conclusion:**
Therefore,
$$\frac{d}{dx} x^n = nx^{n-1}$$
This completes the proof in a simple and clear way.