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If sinbeta is geometric mean between sin...

If `sinbeta` is geometric mean between `sin alpha and cos alpha , ` then `cos 2beta` =

A

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

B

`2sin^2(pi/3-alpha)" or " 2 cos^2(pi/3+alpha)`

C

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

D

`sin^2(pi/3-alpha)" or " 2 cos^2(pi/3+alpha)`

Text Solution

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The correct Answer is:
A
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