1.

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

Answer»

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

ANSWER :A::B


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