已知COSa+COSb+COSy=0,SINa+SINb+SINy=0,求COS(b-y)的值
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已知COSa+COSb+COSy=0,SINa+SINb+SINy=0,求COS(b-y)的值已知COSa+COSb+COSy=0,SINa+SINb+SINy=0,求COS(b-y)的值已知COSa
已知COSa+COSb+COSy=0,SINa+SINb+SINy=0,求COS(b-y)的值
已知COSa+COSb+COSy=0,SINa+SINb+SINy=0,求COS(b-y)的值
已知COSa+COSb+COSy=0,SINa+SINb+SINy=0,求COS(b-y)的值
COS(b-y)=COSbCOSy+SINbSIBy COSa+COSb+COSy=0,(COSb+COSy)=COSa COSb+2COSbCOSy+COSy=COSa COSbCOSy=(COSa-COSb-COSy)/2 同理:SINbSINy=(SINa-SINb-SINy)/2 则COS(b-y)=COSbCOSy+SINbSIBy=(COSa-COSb-COSy)/2+(SINa-SINb-SINy)/2 =(COSa+SINa-COSb-SINb-COSy-SINy)/2 =(1-1-1)/2 =-1/2
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