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For any alpha in R, prove that cos ^(2) ...

For any `alpha in R`, prove that `cos ^(2) (alpha -(pi)/(4))+ cos ^(2) (alpha + (pi)/(12))- cos ^(2) (alpha -(pi)/(12))=(1)/(2)`

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The correct Answer is:
`=(1)/(2)=R.H.S`
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