If cos3θ = sin(θ - 34°), find the value of θ if 3θ is an acute angle.

Sum

cos3θ = sin(θ - 34°)
⇒ sin(90° - 3θ) = sin(θ - 34°)
⇒ 90° - 3θ = θ - 34°
⇒ 4θ = 124°
⇒ θ = 31°.

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