结果为0。
解： (1)直接计算 `cos5°+cos77°+cos149°+cos221°+cos293° =cos5°+cos77°-cos31°-cos41°+cos67° =2cos41°cos36°-2cos36°cos5°+cos67 =2cos36°(cos41°-cos5°)+cos67° =-2cos36°2sin23°sin18°+sin23° =-sin23°(4sin18°cos18°cos36°)/cos18°+sin23° =-sin23°(2sin36°cos36°/cos18°)+sin23° =-sin23°(sin72°/sin72°)+sin23° =-sin23+sin23 =0 (2)向量法 (cos5°,sin5°)+(cos77°,sin77°)+(cos149°,sin149°)+(cos221°,sin221°)+(cos293°,sin293°)=(0,0) 。
答：不查表求三角函数 (cos18度)*(sin36度)的值。 查表也没用. 令x=sin18°, ∵sin54°=cos36°. ∴3x-4x^3=1-2x^2 ...详情>>
答：详情>>
