Question : Given that A and B are second quadrant angles, $\sin A = \frac{1}{3}$ and $\sin B = \frac{1}{5}$, then find the value of $\cos(A-B)$.
Option 1: $\frac{4 \sqrt{3}+1}{15}$
Option 2: $\frac{8 \sqrt{3}-1}{15}$
Option 3: $\frac{8 \sqrt{3}+1}{15}$
Option 4: $\frac{4 \sqrt{3}-1}{15}$
Correct Answer: $\frac{8 \sqrt{3}+1}{15}$
Solution : $\sin A = \frac{1}{3}$ ⇒ $\cos A = \sqrt{1-\sin^2 A} = \sqrt{1-(\frac{1}{9})} = \frac{\sqrt8}{3}$ Also, $\sin B = \frac{1}{5}$ ⇒ $\cos B = \sqrt{1-\sin^2 B} = \sqrt{1-(\frac{1}{25})} = \frac{2\sqrt6}{5}$ Now, $\cos(A-B) = \cos A \cos B + \sin A \sin B$ $= \frac{\sqrt8}{3} × \frac{2\sqrt6}{5} + \frac{1}{3} × \frac{1}{5}$ $= \frac{8\sqrt3+1}{15}$ Hence, the correct answer is $\frac{8\sqrt3+1}{15}$.
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Question : Find the value of $\sqrt{\frac{1-\tan A}{1+\tan A}}$.
Option 1: $\sqrt{\frac{1+\sin 2 A}{\cos 2 A}}$
Option 2: $\sqrt{\frac{1-\sin 2 A}{\cos 2 A}}$
Option 3: $\sqrt{\frac{1+\sin A}{\cos A}}$
Option 4: $\sqrt{\frac{1-\sin A}{\cos A}}$
Question : If $\sin (A-B)=\sin A \cos B–\cos A\sin B$, then $\sin 15°$ will be:
Option 1: $\frac{\sqrt{3}+1}{2\sqrt{2}}$
Option 2: $\frac{\sqrt{3}}{2\sqrt{2}}$
Option 3: $\frac{\sqrt{3}–1}{–\sqrt{2}}$
Option 4: $\frac{\sqrt{3}–1}{2\sqrt{2}}$
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 $\sin A=\frac{1}{2}$, then the value of $(\tan A+\cos A)$ is:
Option 1: $\frac{2}{3 \sqrt{3}}$
Option 2: $\frac{3}{2 \sqrt{3}}$
Option 3: $\frac{5}{2 \sqrt{3}}$
Option 4: $\frac{5}{3 \sqrt{3}}$
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 2: $\sqrt{2} \cos \theta$
Option 3: $\frac{1}{\sqrt{2}} \sin \theta$
Option 4: $\frac{1}{2}\cos \theta$
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