Limits Functions 420E2B
1. **Problem statement:** Find the limits of the following functions as $x \to 0$:
(i) $\lim_{x \to 0} \frac{(1+x)^n - 1}{x}$
(ii) $\lim_{x \to 0} \frac{e^{3x} - 1}{x}$
(iii) $\lim_{x \to 0} \frac{\sin 3x}{5x}$
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2. **Formula and rules:**
- For small $x$, $(1+x)^n \approx 1 + nx$ (Binomial approximation).
- The derivative of $e^{kx}$ at $x=0$ is $k e^{0} = k$.
- The limit $\lim_{x \to 0} \frac{\sin ax}{x} = a$.
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3. **Step-by-step solutions:**
(i) Using the binomial approximation:
$$ (1+x)^n - 1 \approx 1 + nx - 1 = nx $$
So,
$$ \lim_{x \to 0} \frac{(1+x)^n - 1}{x} = \lim_{x \to 0} \frac{nx}{x} = n $$
(ii) Using the exponential limit:
$$ \lim_{x \to 0} \frac{e^{3x} - 1}{x} = \lim_{x \to 0} \frac{e^{3x} - e^0}{x} $$
This is the definition of the derivative of $e^{3x}$ at $x=0$:
$$ = \left. \frac{d}{dx} e^{3x} \right|_{x=0} = 3 e^{0} = 3 $$
(iii) Using the sine limit property:
$$ \lim_{x \to 0} \frac{\sin 3x}{5x} = \frac{1}{5} \lim_{x \to 0} \frac{\sin 3x}{x} = \frac{1}{5} \times 3 = \frac{3}{5} $$
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**Final answers:**
(i) $n$
(ii) $3$
(iii) $\frac{3}{5}$