solve cos3 theta + 8 cos ^ 3 theta =0​

Dear student
We have,cos3θ+8cos3θ=0cos3θ-3cosθsin2θ+8cos3θ=09cos3θ-3cosθsin2θ=03cosθ3cos2θ-sin2θ=03cosθ3cosθ-sinθ3cosθ+sinθ=0Case1: when cosθ=0θ=π2+nπ,nZCase2: 3 cosθ-sinθ=03-tanθ=03=tanθtanθ=tanπ3θ=π3+,nZCase3: 3cosθ+sinθ=03+tanθ=0tanθ=-3tanθ=tan2π3θ=2π3+,nZPlugging all cases, we getθ=π2+,θ=π3+,θ=2π3+,  where nZ
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