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| 1. |
Prove that cos18-sin18 = √2 sin27 |
| Answer» Cos18- Sin18= cos18 - cos72= -2×sin(18+72)/2 × sin (18-72)/2 (using CosC-CosD) = -2 sin45×sin(-27) 2sin45sin27 (sin(-x)=-sinx) =√2×sin27 | |