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If sin(A + B) = sin A cos B + cos A sin B and cos(A - B) = cos A cos B + sin A sin B, find the values of cos 15°. |
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Answer» Given: sin (A + B) = sin A cos B + cos A sin B and cos (A – B) = cos A cos B + sin A sin B Find cos 75° Put A = 45° and B = 30°, then cos 15° = cos 45° cos 30° + sin 45° sin 30° = (1/√2) × (√3/2) + (1/√2) × (1/2) = (√3 / 2√2) + (1/2√2) = (1+√3)/2√2 |
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