(2cos10-sin20)/sin70=____ - 知识问答

(2cos10-sin20)/sin70=_____怎么算?

1个回答

sin20=sin(30-10)
所以 (2cos10°—sin20°)/sin70°
=(2cos10°—sin（30-10)）/sin70°
=(2cos10-(sin30cos10-cos30sin10))/sin70
=(2cos10-1/2cos10+根号3/2sin10)/sin70
=(3/2sin10+根号3/2sin10)/sin70
=根号3（根号3/2cos10+1/2sin10)/sin70
=根号3sin(10+60)/sin70
=根号3

相关问题