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Let θ be the angle between two unit vectors  is perpendicular to  then what is cos θ + cos 2θ equal to?

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Answer (Detailed Solution Below)

Option 1 : 0
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Detailed Solution

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Explanation:

Given:

 and  are perpendicular vectors.

⇒  = 0

⇒ 

⇒ 

Now  are unit vectors

⇒ 

⇒ 1.1 cosθ =1/2

⇒Cosθ = 1/2 

Now

cos2 θ = Cos2θ -1

= 2× 1/4 -1

= 

Now, 

cosθ + cos2θ = 1/2 -1/2 =0

∴The Correct answer is Option a

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