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Let cos beta is the geometric mean betwe...

Let `cos beta` is the geometric mean between `sin alpha and cos alpha ` , where `0 lt alpha lt beta lt pi//2` , then `cos 2beta` is equal to

A

`-2 sin^(2) ((pi)/(4)-alpha)`

B

`-2 cos^(2) ((pi)/(4)+alpha)`

C

`2 sin^(2) ((pi)/(4) + alpha)`

D

`2 cos^(2) ((pi)/(4)-alpha)`

Text Solution

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The correct Answer is:
A, B
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