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Find the general solution of sin θ + sin 3θ + sin 5θ = 0 - Mathematics and Statistics

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Question

Find the general solution of sin θ + sin 3θ + sin 5θ = 0

Sum
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Solution

We have sin θ + sin 3θ + sin 5θ = 0

∴ (sin θ + sin 5θ) + sin 3θ = 0

∴ 2 sin 3θ × cos 2θ + sin 3θ = 0

∴ (2 cos 2θ + 1) sin 3θ = 0

∴ sin 3θ = 0 or cos 2θ = `-1/2`

∴ sin 3θ = 0 or cos 2θ = `cos  (2π)/3`

∴ 3θ = nπ or 2θ = `2nπ ± (2π)/3`, where n ∈ Z.

θ = `(nπ)/3` or θ = `nπ ± π/3`,

where n ∈ Z is the required general solution.

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