cos(a+b)=-2分之1,sin(a+b)=2分之根3,a -b∈(π,2分之3π),a+b∈(0,2分之π),则cos2a的值
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![cos(a+b)=-2分之1,sin(a+b)=2分之根3,a -b∈(π,2分之3π),a+b∈(0,2分之π),则cos2a的值](/uploads/image/z/6845915-11-5.jpg?t=cos%28a%2Bb%29%3D-2%E5%88%86%E4%B9%8B1%2Csin%28a%2Bb%29%3D2%E5%88%86%E4%B9%8B%E6%A0%B93%2Ca+-b%E2%88%88%28%CF%80%2C2%E5%88%86%E4%B9%8B3%CF%80%29%2Ca%2Bb%E2%88%88%280%2C2%E5%88%86%E4%B9%8B%CF%80%29%2C%E5%88%99cos2a%E7%9A%84%E5%80%BC)
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cos(a+b)=-2分之1,sin(a+b)=2分之根3,a -b∈(π,2分之3π),a+b∈(0,2分之π),则cos2a的值
cos(a+b)=-2分之1,sin(a+b)=2分之根3,a -b∈(π,2分之3π),a+b∈(0,2分之π),则cos2a的值
cos(a+b)=-2分之1,sin(a+b)=2分之根3,a -b∈(π,2分之3π),a+b∈(0,2分之π),则cos2a的值
a+b∈(0,π/2) 与 cos(a+b)=-1/2 矛盾,请核题!
由cos(a+b)=cos a cos b-sin a sin b cos(a-b)=cos a cos b+sin a sin b解题设a为锐角,证:1、2分之根3乘cos a + 2分之1乘sin a=cos(6分之π-a)2、cos a-sin a=根号2cos(4分之π+a)
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