Sin(90+10)=sin110=>Sin90cos10+cos90sin10 - sin10=>Cos10-sin10As cos increases from 90 to 0, cos 10(closer to zero) would be a large value(closer to 1)As sin increases from 0 to 90, the value of sin 10 will be closer to zero. So cos10 >sin 10 and thus cos10-sin10 is a positive value