求证sinx+siny=2sin(x+y)/2*cos(x-y)/2
人气：301 ℃ 时间：2020-01-26 02:56:48
解答
sinx+siny=sin[(x+y)/2+(x-y)/2]+sin[(x+y)/2-(x-y)/2]=sin(x+y)/2*cos(x-y)/2+cos(x+y)/2*sin(x-y)/2+sin(x+y)/2*cos(x-y)/2-cos(x+y)/2*sin(x-y)/2=2sin(x+y)/2*cos(x-y)/2其中第2项和第4项互为相反数
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