不查表求三角函数值
已知sin(x+20°)=cos(x+10°)+cos(x-10°),求tanx。
sin(x+20°)=cos(x+10°)+cos(x-10°) →tanx=(2cos10°-sin20°)/cos20° =(cos10°+sin80°-sin20°)/cos20° =(cos10°+2cos50°sin30°)/cos20° =(cos10°+cos50°)/cos20° =2cos30°cos20°/cos20° ∴tanx=2cos30°=√3。
答:结果为0. 解: (1)直接计算 `cos5°+cos77°+cos149°+cos221°+cos293° =cos5°+cos77°-cos31°-cos4...详情>>
答:详情>>