cos105°的值可以通过以下公式计算得出,并保留根号形式: cos105° = cos(180° - 75°) = -cos75° 利用两角和的余弦公式: cos(a + b) = cosacosb - sinasinb 将a设为30°,b设为45°,并代入30°和45°的三角函数值: cos30° = √3/2,sin30° = 1/2,cos45° = 1/√2,sin45° = 1/√...
cos105=(-sqrt(6)+sqrt(2))/4 cos165=-(sqrt(6)+sqrt(2))/4 注：sqrt为根号,/为分数线.
=（根号3-1)^2/2 =(3-2根号3+1)/2 =2-根号3 cos 105° =cos(45°+60°)=cos45°*cos60°-sin45°*sin60° =√2/2*1/2-√2/2*√3/2 =√2/4-√6/4 =(√2-√6)/4