If cos2θ + cos4θ = 1, then the value of sinθ + sin2 θ is:
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 i.e 1
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Understanding Tricks |
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Application cos2θ + cos4θ = 1 .......i) ⇒ cos4θ = 1 - cos2θ So ⇒ cos4θ = sin2θ ........ii) |
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Now cos4θ = sin2θ cos2θ = sinθ (taken root both sides) ........iii) |
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Here Adding eq ii) and eq iii) cos2θ + cos4θ = sin2θ + sinθ Hence ⇒ sin2θ + sinθ = 1 (from eq i) |