Question : If ${\operatorname{cosec} 39^{\circ}} = x$, then the value of $ \frac{1}{\operatorname{cosec}^2 51^{\circ}} +\sin^239^{\circ} +\tan ^251^{\circ} -\frac{1}{\sin ^2 51^{\circ} \sec ^2 39^{\circ}}$ is:
Option 1: $x^2-1$
Option 2: $\sqrt{x^2-1}$
Option 3: $ \sqrt{1-x^2}$
Option 4: $1-x^2$
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Correct Answer: $x^2-1$
Solution : ${\operatorname{cosec} 39^{\circ}} = x$, $ \frac{1}{\operatorname{cosec}^2 51^{\circ}} +\sin^239^{\circ} +\tan ^251^{\circ} -\frac{1}{\sin ^2 51^{\circ} \sec ^2 39^{\circ}}$ $= {\operatorname{sin}^2 51^{\circ}} +\sin^2(90^{\circ}-51^{\circ}) +\tan ^251^{\circ} -\frac{\cos ^2 39^{\circ}}{\sin^2(90^{\circ}-39^{\circ}) }$ $= {\operatorname{sin}^2 51^{\circ}} +\cos^251^{\circ} +\tan ^251^{\circ} -\frac{\cos ^2 39^{\circ}}{\cos ^2 39^{\circ} }$ $=1+\tan ^251^{\circ} -1$ $=\tan ^251^{\circ} $ $=\tan ^2(90^{\circ}-51^{\circ}) $ $=\cot ^239^{\circ} $ $={\operatorname{cosec}^2 39^{\circ}}-1$ [As \(1 + \cot^2\theta =\operatorname{cosec}^2 \theta\)] $=x^2-1$ Hence, the correct answer is $x^2-1$.
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Question : If $x\cos^{2}30^{\circ}\cdot \sin60^{\circ}=\frac{\tan^{2}45^{\circ}\cdot \sec60^{\circ}}{\operatorname{cosec}60^{\circ}}$, then the value of $x$ is:
Option 1: $\frac{1}{\sqrt{3}}$
Option 2: $\frac{1}{\sqrt{2}}$
Option 3: $2\frac{2}{3}$
Option 4: $\frac{1}{2}$
Question : $\left(\frac{\tan ^3 \theta}{\sec ^2 \theta}+\frac{\cot ^3 \theta}{\operatorname{cosec}^2 \theta}+2 \sin \theta \cos \theta\right) \div\left(1+\operatorname{cosec}^2 \theta+\tan ^2 \theta\right), 0^{\circ}<\theta<90^{\circ}$, is equal to:
Option 1: $\operatorname{cosec} \theta \sec \theta$
Option 2: $\operatorname{cosec} \theta$
Option 3: $\sin \theta \cos \theta$
Option 4: $\sec \theta$
Question : If $\operatorname{cosec}\theta+\sin\theta=\frac{5}{2}$, then the value of $(\operatorname{cosec}\theta-\sin\theta)$ is:
Option 1: $-\frac{3}{2}$
Option 2: $\frac{3}{2}$
Option 3: $-\frac{\sqrt{3}}{2}$
Option 4: $\frac{\sqrt{3}}{2}$
Question : Using $\operatorname{cosec}(\alpha+\beta)=\frac{\sec \alpha \times \sec \beta \times \operatorname{cosec} \alpha \times \operatorname{cosec} \beta}{\sec \alpha \times \operatorname{cosec} \beta+\operatorname{cosec} \alpha \times \sec \beta}$, find the value of $\operatorname{cosec} 75°$.
Option 1: $\frac{\sqrt{6}+\sqrt{2}}{4}$
Option 2: $\frac{\sqrt{6}-\sqrt{2}}{4}$
Option 3: $\sqrt{6}-\sqrt{2}$
Option 4: $\sqrt{6}+\sqrt{2}$
Question : If $3 \tan \theta=2 \sqrt{3} \sin \theta, 0^{\circ}<\theta<90^{\circ}$, then the value of $\frac{\operatorname{cosec}^2 2 \theta+\cot ^2 2 \theta}{\sin ^2 \theta+\tan ^2 2 \theta}$ is:
Option 1: $\frac{4}{13}$
Option 2: $\frac{20}{39}$
Option 3: $\frac{4}{3}$
Option 4: $\frac{20}{27}$
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