sinx-siny=-√3/3 cosx-cosy=-1/3 则cos(x-y)
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sinx-siny=-√3/3 cosx-cosy=-1/3 则cos(x-y)
sinx-siny=-√3/3 cosx-cosy=-1/3 则cos(x-y)
sinx-siny=-√3/3 cosx-cosy=-1/3 则cos(x-y)
sinx-siny=-√3/3
两边同时平方得:
sin²x-2sinxsiny+sin²y=1/3 ①
cosx-cosy=-1/3
两边同时平方得:
cos²x-2cosxcosy+cos²y=1/9 ②
由①+②得:
-2sinxsiny-2cosxcosy=4/9
即-2(sinxsiny+cosxcosy)=4/9
-2cos(x-y)=4/9
cos(x-y)=-2/9
答案:-2/9
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