If cos 3θ = α cos θ + β {cos ^3}θ , then (α ,β ) =

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3.Trigonometrical Ratios, Functions and Identities

easy

If $\cos 3\theta = \alpha \cos \theta + \beta {\cos ^3}\theta ,$ then $(\alpha ,\beta ) = $

A

$(3,\,4)$

B

$(4,\,3)$

C

$( - 3,\,4)$

D

$(3,\, - 4)$

Solution

(c) Given that $\cos 3\theta $

$= \alpha \cos \theta + \beta {\cos ^3}\theta $

But $\cos 3\theta = 4{\cos ^3}\theta – 3\cos \theta $

==> $(\alpha ,\beta ) = ( – 3,\,4)$.

Standard 11

Mathematics

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