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数学!急!!!!!!
证明sin(2a+b)/sina-2cos(a+b)=sinb/sina过程!!!!!!!!...
证明sin(2a+b)/sina-2cos(a+b)=sinb/sina 过程!!!!!!!!
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左边
sin(2a+b)/sina-2cos(a+b)
=sin[(a+b)+a]/sina-2cos(a+b)
=[sin(a+b)cosa+cos(a+b)sina]/sina-2cos(a+b)sina/sina
=[sin(a+b)cosa-cos(a+b)sina]/sina
=sin(a+b-a)/sina
=sinb/sina=右边
sin(2a+b)/sina-2cos(a+b)
=sin[(a+b)+a]/sina-2cos(a+b)
=[sin(a+b)cosa+cos(a+b)sina]/sina-2cos(a+b)sina/sina
=[sin(a+b)cosa-cos(a+b)sina]/sina
=sin(a+b-a)/sina
=sinb/sina=右边
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