Answer
The solutions are:
1. \( \theta = \frac{\pi}{6} + k\pi \) for the first equation.
2. \( \theta = -\frac{\pi}{4} + k\pi \) and \( \theta = \frac{3\pi}{4} + k\pi \) for the second equation, and also \( \theta = \frac{\pi}{6} + 2k\pi \) and \( \theta = \frac{5\pi}{6} + 2k\pi \).
Solution
1) Solve
\[
\sqrt{3} \cos \theta - 3 \sin \theta = 0.
\]
**Step 1.** Assume \(\cos\theta \neq 0\) and divide both sides by \(\cos\theta\):
\[
\sqrt{3} - 3 \tan\theta = 0.
\]
**Step 2.** Solve for \(\tan\theta\):
\[
3 \tan\theta = \sqrt{3} \quad \Longrightarrow \quad \tan\theta = \frac{\sqrt{3}}{3}.
\]
**Step 3.** Recognize that
\[
\tan\left(\frac{\pi}{6}\right) = \frac{\sqrt{3}}{3}.
\]
Thus, the general solution is:
\[
\theta = \frac{\pi}{6} + k\pi, \quad k \in \mathbb{Z}.
\]
---
2) Solve
\[
(\cos \theta + \sin \theta)(1-2 \sin \theta)=0.
\]
This equation is satisfied when at least one of the factors is zero.
**Case 1:**
\[
\cos \theta + \sin \theta = 0.
\]
**Step 1.** Rearrange:
\[
\cos \theta = -\sin \theta.
\]
**Step 2.** Divide both sides by \(\cos \theta\) (assuming \(\cos \theta \neq 0\)):
\[
1 = -\tan\theta \quad \Longrightarrow \quad \tan\theta = -1.
\]
**Step 3.** The general solution for \(\tan\theta = -1\) is:
\[
\theta = -\frac{\pi}{4} + k\pi, \quad k \in \mathbb{Z}.
\]
An equivalent way to represent it is:
\[
\theta = \frac{3\pi}{4} + k\pi, \quad k \in \mathbb{Z}.
\]
**Case 2:**
\[
1-2 \sin \theta = 0.
\]
**Step 1.** Solve for \(\sin \theta\):
\[
2\sin \theta = 1 \quad \Longrightarrow \quad \sin \theta = \frac{1}{2}.
\]
**Step 2.** The solutions for \(\sin \theta = \frac{1}{2}\) are:
\[
\theta = \frac{\pi}{6}+2k\pi \quad \text{or} \quad \theta = \frac{5\pi}{6}+2k\pi, \quad k \in \mathbb{Z}.
\]
---
**Final Answers:**
1) For \(\sqrt{3} \cos \theta - 3 \sin \theta = 0\):
\[
\theta = \frac{\pi}{6} + k\pi, \quad k \in \mathbb{Z}.
\]
2) For \((\cos \theta + \sin \theta)(1-2 \sin \theta)=0\):
- Either
\[
\theta = -\frac{\pi}{4}+ k\pi \quad (\text{or equivalently } \theta = \frac{3\pi}{4}+ k\pi), \quad k \in \mathbb{Z},
\]
- or
\[
\theta = \frac{\pi}{6}+ 2k\pi \quad \text{or} \quad \theta = \frac{5\pi}{6}+2k\pi, \quad k \in \mathbb{Z}.
\]
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