sin35°=sin(60°-25°)=sin60°cos25°-cos60°sin25° cos45°=2cos^2(25°)-1=√2/2 解得cos25°=根号sin60°cos25°-cos60°sin25°cos45°=2cos^2(25°)-1=√2/2
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![sin35°=sin(60°-25°)=sin60°cos25°-cos60°sin25° cos45°=2cos^2(25°)-1=√2/2 解得cos25°=根号sin60°cos25°-cos60°sin25°cos45°=2cos^2(25°)-1=√2/2](/uploads/image/z/2487531-3-1.jpg?t=sin35%C2%B0%3Dsin%2860%C2%B0-25%C2%B0%29%3Dsin60%C2%B0cos25%C2%B0-cos60%C2%B0sin25%C2%B0+cos45%C2%B0%3D2cos%5E2%2825%C2%B0%29-1%3D%E2%88%9A2%2F2+%E8%A7%A3%E5%BE%97cos25%C2%B0%3D%E6%A0%B9%E5%8F%B7sin60%C2%B0cos25%C2%B0-cos60%C2%B0sin25%C2%B0cos45%C2%B0%3D2cos%5E2%2825%C2%B0%29-1%3D%E2%88%9A2%2F2)
sin35°=sin(60°-25°)=sin60°cos25°-cos60°sin25° cos45°=2cos^2(25°)-1=√2/2 解得cos25°=根号sin60°cos25°-cos60°sin25°cos45°=2cos^2(25°)-1=√2/2
sin35°=sin(60°-25°)=sin60°cos25°-cos60°sin25° cos45°=2cos^2(25°)-1=√2/2 解得cos25°=根号
sin60°cos25°-cos60°sin25°
cos45°=2cos^2(25°)-1=√2/2
sin35°=sin(60°-25°)=sin60°cos25°-cos60°sin25° cos45°=2cos^2(25°)-1=√2/2 解得cos25°=根号sin60°cos25°-cos60°sin25°cos45°=2cos^2(25°)-1=√2/2
这是些公式,是书上出现过的可以直接用的
倍角公式:
! cos(2α)=(cosα)^2-(sinα)^2=2(cosα)^2-1=1-2(sinα)^2
sin(2α)=2sinα·cosα=2/(tanα+cotα)
tan(2α)=2tanα/(1-tan^2α)
两角和与差的三角函数
cos(α+β)=cosα·cosβ-sinα·sinβ
! cos(α-β)=cosα·cosβ+sinα·sinβ
sin(α±β)=sinα·cosβ±cosα·sinβ
tan(α+β)=(tanα+tanβ)/(1-tanα·tanβ)
tan(α-β)=(tanα-tanβ)/(1+tanα·tanβ)
这是公式
sin(a-b)=sinacosb-cosasinb
cos2a=2cos^2 a-1
sin60°cos25°-cos60°sin25°=sin(60°-25°)=cos45°=2cos^2(25°)-1=√2/2