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AP EAMCET202023 Sep 2020Morning ShiftMathematicsTrigonometric Ratios & IdentitiesActual

Find the general solution of 3 sin 4 θ + cos 4 θ = 1

Options

  1. An π only
  2. Bn π + π 4 only
  3. Cn π - π 4 only
  4. Dn π ,   n π + π 4 and n π - π 4

Correct answer

D. n π ,   n π + π 4 and n π - π 4

Step-by-step solution

3 sin 4 θ + cos 4 θ = 1 ⇒ 3 sin 4 θ = ( 1 - cos 2 θ ) ( 1 + cos 2 θ ) ⇒ 3 sin 4 θ = sin 2 θ · 2 - sin 2 θ sin 2 θ = 0 ,   3 sin 2 θ = 2 - sin 2 θ ⇒ sin 2 θ = 1 2 θ = n π ,   n ∈ z ⇒ θ = n π ± π 4 ,   m ∈ z

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