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Question: Answered & Verified by Expert
If $\cos 3 \theta=\alpha \cos \theta+\beta \cos ^3 \theta$, then $(\alpha, \beta)=$
MathematicsTrigonometric Ratios & IdentitiesJEE Main
Options:
  • A $(3,4)$
  • B $(4,3)$
  • C $(-3,4)$
  • D $(3,-4)$
Solution:
2349 Upvotes Verified Answer
The correct answer is: $(-3,4)$
Given that $\cos 3 \theta=\alpha \cos \theta+\beta \cos ^3 \theta$ But $\cos 3 \theta=4 \cos ^3 \theta-3 \cos \theta \Rightarrow(\alpha, \beta)=(-3,4)$

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