Question : If $\cos ^2 \theta-\sin ^2 \theta=\tan ^2 \phi$, then which of the following is true?
Option 1: $\cos \theta \cos \phi=1$
Option 2: $\cos ^2 \phi-\sin ^2 \phi=\tan ^2 \theta$
Option 3: $\cos ^2 \phi-\sin ^2 \phi=\cot ^2 \theta$
Option 4: $\cos \theta \cos \phi=\sqrt{2}$
Correct Answer: $\cos ^2 \phi-\sin ^2 \phi=\tan ^2 \theta$
Solution : Given, $\cos^2\theta – \sin^2 \theta = \tan^2 \phi$ ⇒ $\frac{\cos^2 \theta – \sin^2\theta}{1} = \frac{\sin^2\phi}{\cos^2 \phi}$ ⇒ $\frac{\cos^2 \theta – \sin^2 \theta}{\cos^2\theta + \sin^2 \theta} = \frac{\sin^2\phi}{\cos^2 \phi}$ By Componendo and Dividendo, ⇒ $\frac{\cos^2 \theta}{–\sin^2 \theta} = \frac{\sin^2 \phi + \cos^2 \phi}{\sin^2 \phi - \cos^2 \phi}$ ⇒ $\frac{–\sin^2\theta}{\cos^2 \theta} = \frac{\sin^2 \phi – \cos^2 \phi}{\sin^2 \phi+ \cos^2 \phi}$ ⇒ $\frac{–\sin^2\theta}{\cos^2 \theta}= \frac{\sin^2\phi – \cos^2 \phi}{1}$ [As $\sin^2\phi + \cos^2\phi=1$] ⇒ $\tan^2 \theta = \cos^2\phi-\sin^2\phi $ Hence, the correct answer is $\tan^2 \theta = \cos^2 \phi-\sin^2 \phi$.
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Question : If $\cos \theta-\sin \theta=\sqrt{2} \sin \theta$, then $(\cos \theta+\sin \theta)$ is:
Option 1: $-\sqrt{2} \cos \theta$
Option 2: $\sqrt{2} \cos \theta$
Option 3: $\sqrt{2} \tan \theta$
Option 4: $-\sqrt{2} \sin \theta$
Question : If $\sin \theta+\cos \theta=\sqrt{2} \cos \theta$, then find $\frac{\sin \theta-\cos \theta}{\sin \theta}$:
Option 1: $-\sqrt{2}$
Option 2: $-1$
Option 3: $1$
Option 4: $\sqrt{2}$
Question : If $\operatorname{cos} \theta+\operatorname{sin} \theta=\sqrt{2} \operatorname{cos} \theta$, find the value of $(\cos \theta-\operatorname{sin} \theta)$
Option 1: $\sqrt{2} \sin \theta$
Option 3: $\frac{1}{\sqrt{2}} \sin \theta$
Option 4: $\frac{1}{2}\cos \theta$
Question : Simplify $\frac{\cos ^4 \theta-\sin ^4 \theta}{\sin ^2 \theta}$.
Option 1: $1-\tan ^2 \theta$
Option 2: $\tan ^2 \theta-1$
Option 3: $\cot ^2 \theta-1$
Option 4: $1-\cot ^2 \theta$
Question : The value of $\frac{2 \cos ^3 \theta-\cos \theta}{\sin \theta-2 \sin ^3 \theta}$ is:
Option 1: $\sec \theta$
Option 2: $\sin \theta$
Option 3: $\cot \theta$
Option 4: $\tan \theta$
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