Question : $\cos^4 A-\sin^4 A$ is equal to:
Option 1: $2 \cos^2 A+1$
Option 2: $1-2 \sin ^2 A$
Option 3: $2 \sin^2 A-1$
Option 4: $-\left(2 \sin^2 A+1\right)$
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Correct Answer: $1-2 \sin ^2 A$
Solution : Given: $\cos^4 A-\sin^4 A$ $= (\cos^2A)^2-(\sin ^2A)^2$ $= (\cos^2A-\sin^2 A)(\cos^2 A+\sin^2 A)$ $= (\cos^2A-\sin^2A)×1$ [$\because \cos^2A+\sin^2A=1$] $=(1-\sin^2A-\sin^2A)$ $= 1-2\sin^2A$ Hence, the correct answer is $1-2\sin^2A$.
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Question : What is the value of $\frac{\sin \theta+\cos \theta}{\sin \theta-\cos \theta}+\frac{\sin \theta-\cos \theta}{\sin \theta+\cos \theta}$?
Option 1: $\frac{1}{\left(\sin ^2 \theta-\cos ^2 \theta\right)}$
Option 2: $2\left(\sin ^2 \theta-\cos ^2 \theta\right)$
Option 3: $\frac{2}{\left(\sin ^2 \theta-\cos ^2 \theta\right)}$
Option 4: $\sin ^2 \theta-\cos ^2 \theta$
Question : Simplify the given equation: $(1+\tan ^2 A)(1+\cot ^2 A)=?$
Option 1: $\frac{1}{\cos ^2 A\left(1+\sin ^2 A\right)}$
Option 2: $\frac{1}{\sin ^2 A\left(1-\sin ^2 A\right)}$
Option 3: $\frac{1}{\sin ^2 A+\operatorname{cosec}^2 A}$
Option 4: $\frac{1}{\sin ^2 A\left(1+\cos ^2 A\right)}$
Question : If $\sin A+\sin ^2 A=1$, then the value of the expression $\left(\cos ^2 A+\cos ^4 A\right)$ is
Option 1: $\frac{3}{2}$
Option 2: $1$
Option 3: $2$
Option 4: $\frac{1}{2}$
Question : The value of expression $4\left(\sin ^6 A+\cos ^6 A\right)-6\left(\sin ^4 A+\cos ^4 A\right)+8$ is:
Option 1: 4
Option 2: 8
Option 3: 7
Option 4: 6
Question : The given expression is equal to $\frac{\sin^4 A+\cos^4 A}{1-2 \sin^2 A \cos^2 A}$:
Option 1: 1
Option 2: –1
Option 3: 0
Option 4: 2
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