\(sin (\theta + 30°) = cos 15°\) হলে, \(cos 2\theta\) এর মান কতো ? Madhyamik 2025
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\(sin (\theta + 30°) = cos 15°\)
বা, \(sin (\theta + 30°) = sin(90° - 15°)\)
বা, \(\theta + 30° = 90° - 15°\)
বা, \(\theta = 75°- 30° \)
বা, \(\theta = 45°\)
বা, \(2\theta = 90°\)
\(\therefore cos 2\theta=cos 90° =0\) [Answer]

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