为什么sinx*cosy-cosx*siny=sin(x-y)
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为什么sinx*cosy-cosx*siny=sin(x-y)
这个高中课本上有证明的.
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再答: �Ƽ�һ��������֤���� �ڵ�λԲ��ȡ����M N����x��ļнǷֱ���x,pi/2+y ��M��cosx,sinx��,N(-siny,cosy) ��OM��ON��= cos(OM,ON)=cos(pi/2+y-x)=sin(x-y)=OM���ON/(|OM||ON|) �� sin(x-y)=sinxcosy-cosxsiny ��-y�滻y�ɵã�sin(x+y)=sinxcosy+cosxsiny ֤�� ���ƵĿɵõ�cos(x+y)�Ĺ�ʽ
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再问: ��û��α�
再答: �Ƽ�һ��������֤���� �ڵ�λԲ��ȡ����M N����x��ļнǷֱ���x,pi/2+y ��M��cosx,sinx��,N(-siny,cosy) ��OM��ON��= cos(OM,ON)=cos(pi/2+y-x)=sin(x-y)=OM���ON/(|OM||ON|) �� sin(x-y)=sinxcosy-cosxsiny ��-y�滻y�ɵã�sin(x+y)=sinxcosy+cosxsiny ֤�� ���ƵĿɵõ�cos(x+y)�Ĺ�ʽ
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