Q49 / 160 · AP EAMCET 2022 (04 Jul Shift 2) · Mathematics

A true statement among the following identities is

  • Correct answer
    A
    sin5θ=16cos4θsinθ-12cos2θsinθ+sinθ
  • B
    sin5θ=16cos4θ-12cos2θ+1
  • C
    sin5θ=16cos4θsinθ+12cos2θsinθ-sinθ
  • D
    sin5θ=16cos4θsinθ+12cos2θsinθ+sinθ

Solution

We have,

sin5θ=sin3θ+2θ

⇒sin5θ=sin3θcos2θ+cos3θsin2θ

⇒sin5θ=3sinθ-4sin3θ2cos2θ-1+4cos3θ-3cosθ2sinθcosθ

⇒sin5θ=6sinθcos2θ-3sinθ-8sin3θcos2θ+4sin3θ+8sinθcos4θ-6sinθcos2θ

⇒sin5θ=-3sinθ-8sin2θsinθcos2θ+4sin2θsinθ+8sinθcos4θ

⇒sin5θ=-3sinθ-81-cos2θsinθcos2θ+41-cos2θsinθ+8sinθcos4θ

⇒sin5θ=-3sinθ-8sinθcos2θ+8sinθcos4θ+4sinθ-4sinθcos2θ+8sinθcos4θ

⇒sin5θ=16sinθcos4θ-12sinθcos2θ+sinθ

Hence, the correct answer is option: 'A'.

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