两角差的余弦的计算题、、急...cos105°=cos165°=cos(5π/12)=cos(17π/12)=cos70°cos40°+sin70°sin40°=cos100°cos20°-sin100°sin20°=
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![两角差的余弦的计算题、、急...cos105°=cos165°=cos(5π/12)=cos(17π/12)=cos70°cos40°+sin70°sin40°=cos100°cos20°-sin100°sin20°=](/uploads/image/z/10251679-31-9.jpg?t=%E4%B8%A4%E8%A7%92%E5%B7%AE%E7%9A%84%E4%BD%99%E5%BC%A6%E7%9A%84%E8%AE%A1%E7%AE%97%E9%A2%98%E3%80%81%E3%80%81%E6%80%A5...cos105%C2%B0%3Dcos165%C2%B0%3Dcos%EF%BC%885%CF%80%2F12%EF%BC%89%3Dcos%EF%BC%8817%CF%80%2F12%EF%BC%89%3Dcos70%C2%B0cos40%C2%B0%2Bsin70%C2%B0sin40%C2%B0%3Dcos100%C2%B0cos20%C2%B0-sin100%C2%B0sin20%C2%B0%3D)
两角差的余弦的计算题、、急...cos105°=cos165°=cos(5π/12)=cos(17π/12)=cos70°cos40°+sin70°sin40°=cos100°cos20°-sin100°sin20°=
两角差的余弦的计算题、、急...
cos105°=
cos165°=
cos(5π/12)=
cos(17π/12)=
cos70°cos40°+sin70°sin40°=
cos100°cos20°-sin100°sin20°=
两角差的余弦的计算题、、急...cos105°=cos165°=cos(5π/12)=cos(17π/12)=cos70°cos40°+sin70°sin40°=cos100°cos20°-sin100°sin20°=
cos105°= cos(45°+60°)=cos45°cos60°-sin45°*sin60°=√2/4-√6/4=(√2-√6)/4
cos165°=cos(45°+120°)=cos45°cos120°-sin45°sin120°=-√2/4-√6/4=-(√2+√6)/4
cos(5π/12)= cos(π/6+π/4)=cosπ/6cosπ/4-sinπ/6sinπ/4=√6/4-√2/4=(√6-√2)/4
cos(17π/12)=cos(π+5π/12)=-(√6-√2)/4
cos70°cos40°+sin70°sin40°
= cos(70°-40°)=√3/2
cos100°cos20°-sin100°sin20°
=cos(100°+20°)=-1/2