Question : If $\cos ^4 \alpha-\sin ^4 \alpha=\frac{5}{6}$, then the value of $2 \cos ^2 \alpha-1$ is:
Option 1: $\frac{11}{6}$
Option 2: $\frac{5}{6}$
Option 3: $\frac{6}{11}$
Option 4: $\frac{6}{5}$
Correct Answer: $\frac{5}{6}$
Solution : Given: $\cos ^4 \alpha-\sin ^4 \alpha=\frac{5}{6}$ ⇒ $(\cos ^2 \alpha)^2-(\sin ^2 \alpha)^2=\frac{5}{6}$ ⇒ $(\cos ^2 \alpha-\sin ^2 \alpha)(\cos ^2 \alpha+\sin ^2 \alpha)=\frac{5}{6}$ ⇒ $(\cos ^2 \alpha-\sin ^2 \alpha)=\frac{5}{6}$ [As $\cos ^2 \alpha+\sin ^2 \alpha=1$] ⇒ $\cos^2\alpha - 1+\cos^2\alpha=\frac{5}{6}$ [As $\sin^2\alpha=1-\cos^2\alpha$] $\therefore2\cos ^2 \alpha-1=\frac{5}{6}$ Hence, the correct answer is $\frac{5}{6}$.
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Question : If $\alpha$ is an acute angle and $2\sin \alpha+15\cos^2\alpha=7$, then the value of $\cot \alpha$ is:
Option 1: $\frac{4}{3}$
Option 2: $\frac{4}{5}$
Option 3: $\frac{5}{4}$
Option 4: $\frac{3}{4}$
Question : If $\sin \theta+\cos \theta=\frac{\sqrt{11}}{3}$, then the value of $(\cos \theta-\sin \theta)$ is:
Option 1: $\frac{\sqrt{5}}{3}$
Option 2: $\frac{7}{3}$
Option 3: $\frac{5}{3}$
Option 4: $\frac{\sqrt{7}}{3}$
Question : If $\cos \theta+\sec \theta=2$, then the value of $\sin ^6 \theta+\cos ^6 \theta$ is:
Option 1: $\frac{1}{3}$
Option 2: $0$
Option 3: $1$
Option 4: $\frac{1}{2}$
Question : If $\sin \theta+\cos \theta=\frac{\sqrt{11}}{3}$, then what is $\sin \theta-\cos \theta$?
Option 1: $\frac{\sqrt{7}}{4}$
Option 2: $\frac{\sqrt{7}}{3}$
Option 3: $\frac{\sqrt{5}}{3}$
Option 4: $\frac{\sqrt{5}}{2}$
Question : If $x=\frac{2 \sin \theta}{(1+\cos \theta+\sin \theta)}$, then the value of $\frac{1-\cos \theta+\sin \theta}{(1+\sin \theta)}$ is:
Option 1: $\frac{x}{(1+x)}$
Option 2: $x$
Option 3: $\frac{1}{x}$
Option 4: $\frac{(1+x)}{x}$
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