If $\cos 3\theta = \alpha \cos \theta + \beta {\cos ^3}\theta ,$ then $(\alpha ,\beta ) = $
If $\cos 3\theta = \alpha \cos \theta + \beta {\cos ^3}\theta ,$ then $(\alpha ,\beta ) = $
- A
$(3,\,4)$
- B
$(4,\,3)$
- C
$( - 3,\,4)$
- D
$(3,\, - 4)$
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