Limits Trigonometric
1. **State the problems:**
Find the limits:
$$\lim_{\theta \to 0} \frac{\tan \theta}{\theta^2 \cot 36}$$
and
$$\lim_{\theta \to 0} \frac{\theta \cot 4\theta}{\sin^2 \theta \cot^2 2\theta}$$
2. **Recall important formulas and rules:**
- As $\theta \to 0$, $\tan \theta \approx \theta$.
- As $\theta \to 0$, $\sin \theta \approx \theta$.
- $\cot x = \frac{1}{\tan x}$.
- Constants like $\cot 36$ are just numbers.
3. **Solve the first limit:**
$$\lim_{\theta \to 0} \frac{\tan \theta}{\theta^2 \cot 36} = \lim_{\theta \to 0} \frac{\tan \theta}{\theta^2} \cdot \frac{1}{\cot 36}$$
Using $\tan \theta \approx \theta$ near zero:
$$= \lim_{\theta \to 0} \frac{\theta}{\theta^2} \cdot \frac{1}{\cot 36} = \lim_{\theta \to 0} \frac{1}{\theta} \cdot \frac{1}{\cot 36}$$
As $\theta \to 0$, $\frac{1}{\theta} \to \infty$, so the limit diverges to infinity.
**Answer:** The first limit does not exist (diverges to infinity).
4. **Solve the second limit:**
$$\lim_{\theta \to 0} \frac{\theta \cot 4\theta}{\sin^2 \theta \cot^2 2\theta}$$
Rewrite cotangents:
$$= \lim_{\theta \to 0} \frac{\theta \cdot \frac{1}{\tan 4\theta}}{(\sin \theta)^2 \cdot \left(\frac{1}{\tan 2\theta}\right)^2} = \lim_{\theta \to 0} \frac{\theta}{\tan 4\theta} \cdot \frac{\tan^2 2\theta}{\sin^2 \theta}$$
Use approximations near zero:
- $\tan 4\theta \approx 4\theta$
- $\tan 2\theta \approx 2\theta$
- $\sin \theta \approx \theta$
Substitute:
$$= \lim_{\theta \to 0} \frac{\theta}{4\theta} \cdot \frac{(2\theta)^2}{\theta^2} = \lim_{\theta \to 0} \frac{1}{4} \cdot \frac{4\theta^2}{\theta^2} = \frac{1}{4} \cdot 4 = 1$$
**Answer:** The second limit equals 1.
**Final answers:**
- First limit: Does not exist (diverges to infinity).
- Second limit: 1.