Fewpal
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How do you solve  cos3 x = cos x ?

1 Answer

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Best answer

Answer:

x=kπ/2,k=0,±1,±2,⋯

Explanation:

cos3x=cosx or
(cos2x−1)cosx=−sin2xcosx=0

So we need the x such that make

cosx=0 or sinx=0 or

cosx=0→x=π/2+2kπ,k=0,±1,±2,⋯
sinx=0→x=π+2kp,k=0,±1,±2,⋯

or x=kπ/2,k=0,±1,±2,⋯

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