化简sin(x+y)sin(x-y)-cos(x+y)cos(x-y)的结果是?

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化简sin(x+y)sin(x-y)-cos(x+y)cos(x-y)的结果是?化简sin(x+y)sin(x-y)-cos(x+y)cos(x-y)的结果是?化简sin(x+y)sin(x-y)-c

化简sin(x+y)sin(x-y)-cos(x+y)cos(x-y)的结果是?
化简sin(x+y)sin(x-y)-cos(x+y)cos(x-y)的结果是?

化简sin(x+y)sin(x-y)-cos(x+y)cos(x-y)的结果是?
sin(x+y)sin(x-y)-cos(x+y)cos(x-y)
=-cos[(x+y)+(x-y)]
=-cos2x

原式=-[cos(x+y)cos(x-y)-sin(x+y)sin(x-y)]
=-cos[(x+y)+(x-y)]
=-cos2x