来自陶晶的问题
【1,cos20°-cos40°-cos80°=?】
1,cos20°-cos40°-cos80°=?
1回答
2020-03-06 14:29
【1,cos20°-cos40°-cos80°=?】
1,cos20°-cos40°-cos80°=?
cos20°-cos40°-cos80°
=cos(30°-10°)-cos(30°+10°)-sin10°
=cos30°*cos10°+sin30°*sin10°-cos30°cos10°+sin30°sin10°-sin10°
=2sin30°sin10°-sin10°
=2*(1/2)*sin10°-sin10°
=sin10°-sin10°
=0