Question : What is the value of the expression $\cos 2 A \cos 2 B+\sin ^2(A-B)-\sin ^2(A+B)$?
Option 1: $\sin (2 A-2 B)$
Option 2: $\sin (2 A+2 B)$
Option 3: $\cos (2 A+2 B)$
Option 4: $\cos (2 A-2 B)$
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Correct Answer: $\cos (2 A+2 B)$
Solution : Given, $\cos(2A)\cos(2B)+\sin^2(A-B)-\sin^2(A+B)$ $=\cos(2A)\cos(2B) - [\sin^2(A + B) - \sin^2(A - B)]$ $=\cos(2A)\cos(2B) - [\sin(A + B) + \sin(A - B)][\sin(A + B) - \sin(A - B)]$ Using Identities: $\sin C + \sin D = 2\sin \frac{C+D}{2}\cos \frac{C-D}{2}$ and $\sin C - \sin D = 2\cos \frac{C+D}{2}\sin \frac{C-D}{2}$, we get, $=\cos(2A)\cos(2B) - [2\sin \frac{(A + B)+(A-B)}{2}\cos \frac{(A + B)-(A-B)}{2}][2\cos \frac{(A + B)+(A-B)}{2}\sin \frac{(A + B)-(A-B)}{2}]$ $=\cos(2A)\cos(2B) - (2\sin A\cos B)(2\cos A\sin B)$ $=\cos{2A}\cos{2B}-\sin{2A}\sin{2B}$ $=\cos (2A + 2B)$ Hence, the correct answer is $\cos (2A + 2B)$.
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Question : What is the value of the given expression if $3\cot A=\frac{7}{3}$? $\frac{3 \cos A+2 \sin A}{3 \cos A-2 \sin A}$
Option 1: $\frac{2}{3}$
Option 2: $\frac{1}{3}$
Option 3: $13$
Option 4: $1$
Question : If $\cos A+\cos^2 A=1$, then the value of $\sin^4 A+\sin^6 A$ is:
Option 1: $2$
Option 2: $\cos \mathrm{A}$
Option 3: $1$
Option 4: $\sin A$
Question : Which of the following options gives an expression equivalent to $\sin \ (A + B)$?
Option 1: $\cos\ A \cos\ B - \sin \ A \sin \ B$
Option 2: $\sin\ A \cos \ B + \cos\ A\ \sin \ B$
Option 3: $\cos \ A \cos\ B+\sin\ A \sin \ B$
Option 4: $\sin \ A \cos \ B - \cos \ A \sin \ B$
Question : Solve the following to find its value in terms of trigonometric ratios. $(\sin A + \cos A)(1 - \sin A \cos A)$
Option 1: $\sin^3A+\cos^3A$
Option 2: $\sin^2A-\cos^2A$
Option 3: ${[\cos A-\sin A]\left[\sin ^2 A+\cos ^2 A\right]}$
Option 4: $\sin^3A-\cos^3A$
Question : Find the value of the following expression. $5\left(\sin ^4 \theta+\cos ^4 \theta\right)+3\left(\sin ^6 \theta+\cos ^6 \theta\right)+19 \sin ^2 \theta \cos ^2 \theta$
Option 1: 8
Option 2: 5
Option 3: 6
Option 4: 7
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