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| 1. |
Cos18°-sin18°=√2sin27° |
| 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 | |