已知sina-cosb+siny=0,cosa+cosb-cosy=0,求sin(a-b)的值
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已知sina-cosb+siny=0,cosa+cosb-cosy=0,求sin(a-b)的值
你公式输入错了吧,应该是cosa+sinb-cosy=0吧
siny=cosb-sina
cosy=cosa+sinb
1 =sin2y +cos2y
= (cosb- sina)2+ (cosa+sinb)2
= cos2b -2 cosb sina +sin2a+ cos2a+2 cosa sinb+ sin2b
=2 cosa sinb-2 cosb sina+ sin2a+ cos2a+ sin2b + cos2b
=2-2sin(a-b)
所以sin(a-b)=1/2
有些2是平方,注意看清哦
siny=cosb-sina
cosy=cosa+sinb
1 =sin2y +cos2y
= (cosb- sina)2+ (cosa+sinb)2
= cos2b -2 cosb sina +sin2a+ cos2a+2 cosa sinb+ sin2b
=2 cosa sinb-2 cosb sina+ sin2a+ cos2a+ sin2b + cos2b
=2-2sin(a-b)
所以sin(a-b)=1/2
有些2是平方,注意看清哦
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