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| 1. |
Sin 40 degree - cos 70 degree = √3. Cos 80 degree |
| Answer» Sin40-cos70=Sin40-cos(90-20)=Sin40-sin20=2cos40+20/2×sin40-20/2=2cos60/2×sin20/2=2×√3/2×sin10=√3sin(90-80)√3cos10 | |