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Express sin⁡θ in terms of cot⁡θ, where θ is an acute angle.
Question

Express sin⁡θ in terms of cot⁡θ, where θ is an acute angle.

A.

1+cot2θ1+\cot^2⁡θ​​

B.

1+cot2θ\sqrt{1+cot^2⁡θ}​​

C.

11+cot2θ\frac{1}{1+\cot^2⁡θ}​​

D.

11+cot2θ\frac{1}{\sqrt{1+\cot^2⁡θ}}​​

Correct option is D

Given: 
θ\theta  is acute angle;
To express sinθ\sin \theta in terms of cotθ\cot \theta 
Formula Used: 
cotθ=cosθsinθ\cot \theta = \frac{\cos \theta}{\sin \theta} 
sin2θ+cos2θ=1\sin^2 \theta + \cos^ 2\theta = 1  
Solution: 
cotθ=cosθsinθ cosθ=sinθcotθ\cot \theta = \frac{\cos \theta}{\sin \theta} \implies \cos \theta = \sin \theta \cdot \cot \theta  
Now, 
sin2θ+cos2θ=1 sin2θ+(sinθcotθ)2=1 sin2θ(1+cot2θ)=1 sin2θ=11+cot2θ  sinθ=11+cot2θ\sin^2 \theta + \cos^ 2\theta = 1 \\ \ \\ \sin^2 \theta + (\sin \theta \cdot \cot \theta)^2 = 1 \\ \ \\ \sin^2 \theta ( 1+ \cot^2 \theta) = 1 \\ \ \\ \sin^2 \theta = \frac{1}{1 + \cot^2 \theta} \\ \ \\ \implies \bf \sin \theta = \frac{1}{\sqrt{1 + \cot^2 \theta}} ​​​​

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