sinx-siny=2sin(x-y)/2*cos(x+Y)/2这怎么算出来的啊?

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sinx-siny=2sin(x-y)/2*cos(x+Y)/2这怎么算出来的啊?

sinx-siny=2sin(x-y)/2*cos(x+Y)/2这怎么算出来的啊?
sinx-siny=2sin(x-y)/2*cos(x+Y)/2
这怎么算出来的啊?

sinx-siny=2sin(x-y)/2*cos(x+Y)/2这怎么算出来的啊?
设a=(x+y)/2 ,b=(x–y)/2
那么 x=a+b ,y=a–b
所以
sinx–siny=sin(a+b)–sin(a–b)
=sina*cosb+cosa*sinb– (sina*cosb–cosa*sinb)
= sina*cosb+cosa*sinb–sina*cosb+cosa*sinb
=2 cosa*sinb
=2sin(x–y)/2*cos(x+y)/2

sinx-siny=sin(x+y)/2cos(x-y)/2+cos(x+y)/2sin(x-y)/2-sin(x+y)/2cos(x-y)/2+cos(x+y)/2sin(x-y)/2=2cos(x-y)/2sin(x+y)/2
回答完毕

右边有两个“/2”，看不懂什么意思。 不过我觉得应该把右边的展开并整理，就可得到左边的！希望帮得到你。

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