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Prove that : cos 24° + cos 55° + cos 125° + cos 204° + cos 300° = \(\cfrac12\) |
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Answer» LHS = = cos 24° + cos 55° + cos 125° + cos 204° + cos 300° = cos 24° + cos (90° × 1 – 35°) + cos (90° × 1 + 35°) + cos (90° × 2 + 24°) + cos (90° × 3 + 30°) We know that when n is odd, cos → sin. = cos 24° + sin 35° - sin 35° - cos 24° + sin 30° = 0 + 0 + 1/2 = 1/2 = RHS Hence proved. |
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