证明sin(x+y)sin(x-y)=sin²x-sin²y
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解决时间 2021-08-22 01:19
- 提问者网友：皆是孤独
- 2021-08-21 05:40
证明sin(x+y)sin(x-y)=sin²x-sin²y
最佳答案
- 五星知识达人网友：独行浪子会拥风
- 2021-08-21 06:20
解：sin(x+y)sin(x-y)
=-1/2(cos(x+y+x-y)—cos(x+y-x+y))
=-1/2(cos2x—cos2y)
=-1/2(1-2（sinx）^2-1+2(siny）^2)
=（sinx）^2-(siny）^2
=-1/2(cos(x+y+x-y)—cos(x+y-x+y))
=-1/2(cos2x—cos2y)
=-1/2(1-2（sinx）^2-1+2(siny）^2)
=（sinx）^2-(siny）^2
全部回答
- 1楼网友：何以畏孤独
- 2021-08-21 06:45
拆开就行了、、刚好是平方差
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