Functions 1 Question 8

8. Let f(θ)=sinθ(sinθ+sin3θ). Then, f(θ)

(2000, 1M)

(a) 0, only when θ0

(b) 0, for all real θ

(c) 0, for all real θ

(d) 0, only when θ0

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Answer:

Correct Answer: 8. A

Solution:

  1. It is given,

f(θ)=sinθ(sinθ+sin3θ)=(sinθ+3sinθ4sin3θ)sinθ=(4sinθ4sin3θ)sinθ=sin2θ(44sin2θ)=4sin2θcos2θ=(2sinθcosθ)2=(sin2θ)20

which is true for all θ.



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