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sin(x-y)sin(x+y)-cos(x-y)cos(x+y)
人气:129 ℃ 时间:2020-05-22 10:33:03
解答
sin(x-y)sin(x+y)-cos(x-y)cos(x+y)
=-cos[(x-y)+(x+y)]
=-cos2x
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