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If A = 60° and B = 30°, verify that cos (A − B) = cos A cos B + sin A sin B. |
Answer» cos (A – B) = cos A cos B + sin A sin B If A = 60° and B = 30°, then Verify: cos (30°) = cos 60° cos 30° + sin 60° sin 30° R.H.S. = cos 60° cos 30° + sin 60° sin 30° = (1/2) × (√3/2) + (√3/2)(1/2) = (√3/4) + (√3/4) = √3/2 = cos 30° = L.H.S. |
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