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If cosec α = √2, evaluate (2sin2⁡α+3cos2⁡α)(cosec2α+cot2α)\frac{(2 sin²⁡α+3 cos²⁡α)}{(cosec^2 α+cot^2 α)}(cosec2α+cot2α)(2sin2⁡α+3cos2⁡α)​​​
Question

If cosec α = √2, evaluate (2sin2α+3cos2α)(cosec2α+cot2α)\frac{(2 sin²⁡α+3 cos²⁡α)}{(cosec^2 α+cot^2 α)}​​

A.

5/6

B.

5/12

C.

5/3

D.

5/2

Correct option is A

Given:

cosecα=2cosec \alpha = \sqrt{2}​​

Formula used:

cosecα=1sinα cosec \alpha = \frac{1}{sin \alpha}

sinα=1/2\sin \alpha = 1/\sqrt{2}​​

sin2α+cos2α=1\sin^2 \alpha + \cos^2 \alpha = 1​​

cosα=1sin2α\cos \alpha = \sqrt{1 - \sin^2 \alpha}​​

Solution:

sinα=12,sosin2α=12\sin \alpha = \frac{1}{\sqrt{2}} , so \sin^2 \alpha =\frac{ 1}{2}​​

cos2α=112=12\cos^2 \alpha = 1 -\frac{ 1}{2}= \frac{1}{2}​​

2sin2α+3cosαcosec2α+cot2α\frac{2\sin^2 \alpha + 3\cos \alpha}{\cosec^2 \alpha + \cot^2 \alpha}​​

First, calculate the numerator:

Numerator = 2sin2α+3cos2α2\sin^2 \alpha + 3\cos^2 \alpha​​

Numerator = 2×12+3×122\times\frac{1}{2} + 3\times\frac{1}{{2}}​​

Numerator = 1+32=2.51 + \frac{3}{{2}} = 2.5​​

Now, calculate the denominator:

Denominator = cosec2α+cot2α\cosec^2 \alpha + \cot^2 \alpha​​

We know cosecα=2cosec \alpha = \sqrt{2}​​

cosec2α=(2)2=2\cosec^2 \alpha = (\sqrt{2})^2 = 2​​

cotα=cosαsinα=1212=1\cot \alpha = \frac{cos \alpha }{\sin \alpha} =\frac{\frac{ 1}{\sqrt{2}}} { \frac{1}{\sqrt{2}}}= 1​​

cot2α=1\cot^2 \alpha = 1​​

Denominator = 2 + 1 = 3

Finally, the expression becomes:

Result=2.53=56\text{Result} = \frac{2.5}{3} = \frac{5}{6}​​

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