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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° Verify: cos (90°) = 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) = 0 = cos 90° = L.H.S. |
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