2cos3θ = 1 হলে, θ -এর মান (a) 10° (b) 15° (c) 20° (d) 30°

Answer: C
\(2cos3\theta=1\)
বা, \(cos3\theta=\cfrac{1}{2}=cos60°\)
\(\therefore \theta=\cfrac{60°}{3}=20°\)

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