Question :
If $\tan2\theta\tan3\theta=1$ where $0°<\theta<90°$, then the value of $\theta$ is:
Option 1: $22\frac{1}{2}°$
Option 2: $18°$
Option 3: $24°$
Option 4: $30°$
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Correct Answer: $18°$
Solution : Given: $\tan2\theta\tan3\theta=1$ ⇒ $\tan3\theta=\frac{1}{\tan2\theta}$ ⇒ $\tan3\theta=\cot2\theta$ ⇒ $\tan3\theta=\tan(90°–2\theta)$ ⇒ $3\theta=(90°-2\theta)$ ⇒ $5\theta=90°$ $\therefore\theta=18°$ Hence, the correct answer is $18°$.
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Question : If $(r\cos \theta -\sqrt{3})^{2}+(r\sin \theta -1)^{2}=0$, then the value of $\frac{r\tan \theta +\sec \theta}{r\sec \theta +\tan\theta}$ is equal to:
Option 1: $\frac{4}{5}$
Option 2:
$\frac{5}{4}$
Option 3:
$\frac{\sqrt{3}}{4}$
Option 4:
$\frac{\sqrt{5}}{4}$
Question : If $0^{\circ} < \theta < 90^{\circ}$ and $2 \sin^{2}\theta +3\cos\theta =3$, then the value of $\theta$ is:
Option 1: 30°
Option 2: 60°
Option 3: 45°
Option 4: 75°
Question : If $\sin (\theta +18^{\circ})=\cos 60^{\circ}(0< \theta < 90^{\circ})$, then the value of $\cos 5\theta$ is:
Option 1: $\frac{1}{2}$
Option 2: $0$
Option 3: $\frac{1}{\sqrt{2}}$
Option 4: $1$
Question : If $\sin(A+B)=\sin A\cos B+\cos A \sin B$, then the value of $\sin75°$ is:
Option 1: $\frac{\sqrt{3}+1}{\sqrt{2}}$
$\frac{\sqrt{2}+1}{2\sqrt{2}}$
$\frac{\sqrt{3}+1}{2\sqrt{2}}$
$\frac{\sqrt{3}+1}{2}$
Question : Which of the following is a value of $\theta$, when $\cos ^2 \theta-2+\cos \theta=0$?
Option 1: 60°
Option 2: 90°
Option 3: 30°
Option 4: 0°
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