Question : If $2(\cos^{2}\theta-\sin^{2}\theta)=1$; ($\theta$ is a positive acute angle), then $\cot\theta$ is equal to:
Option 1: $–\sqrt{3}$
Option 2: $\frac{1}{\sqrt{3}}$
Option 3: $1$
Option 4: $\sqrt{3}$
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Correct Answer: $\sqrt{3}$
Solution : Given: $2(\cos^{2}\theta-\sin^{2}\theta)=1$ ⇒ $\cos^{2}\theta-(1-\cos^{2}\theta)=\frac{1}{2}$ ⇒ $2\cos^{2}\theta=1+\frac{1}{2}$ ⇒ $\cos^{2}\theta=\frac{3}{2×2}$ ⇒ $\cos\theta=\frac{\sqrt{3}}{2}$ We know that [$\cos30°=\frac{\sqrt{3}}{2}$] ⇒ $\cos\theta=\cos30°$ $\therefore\theta=30°$ Then, $\cot30°=\sqrt{3}$ Hence, the correct answer is $\sqrt{3}$.
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Question : If $\theta$ is an acute angle and $\sin \theta \cos \theta=2 \cos ^3 \theta-\frac{1}{4} \cos \theta$, then the value of $\sin \theta$ is:
Option 1: $\frac{\sqrt{15}-1}{8}$
Option 2: $\frac{\sqrt{15}-1}{4}$
Option 3: $\frac{\sqrt{15}+1}{4}$
Option 4: $\frac{\sqrt{15}-1}{2}$
Question : If $2\left (\cos^{2}\theta-\sin ^{2}\theta \right)=1$; ($\theta$ is a positive acute angle), then $\cot\theta$ is equal to:
Option 1: $-\sqrt3$
Option 2: $1\frac{1}{\sqrt3}$
Option 4: $\sqrt3$
Question : If $\theta$ is a positive acute angle and $4\cos ^{2}\theta -4\cos \theta +1=0$, then the value of $\tan (\theta -15^{\circ})$is equal to:
Option 1: $0$
Option 2: $1$
Option 3: $\sqrt{3}$
Option 4: $\frac{1}{\sqrt{3}}$
Question : If $\sec \theta+\tan \theta=\frac{1}{\sqrt{3}}$, then the positive value of $\cot \theta+\cos \theta$ is:
Option 1: $\frac{3 \sqrt{3}}{2}$
Option 2: $\frac{\sqrt{3}}{2}$
Option 3: $\frac{2}{3 \sqrt{3}}$
Option 4: $\frac{2}{\sqrt{3}}$
Question : The value of $\frac{\sin\theta-2\sin^{3}\theta}{2\cos^{3}\theta-\cos\theta}$ is equal to:
Option 1: $\sin\theta$
Option 2: $\cos\theta$
Option 3: $\tan\theta$
Option 4: $\cot\theta$
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