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  • 證明sinx+siny+sinz-sin(x+y+z)=4sin((x+y)/2)sin((x+y)/2)sin((x+y)/2)

    證明sinx+siny+sinz-sin(x+y+z)=4sin((x+y)/2)sin((x+y)/2)sin((x+y)/2)
    其他人氣:476 ℃時間:2020-03-25 01:06:15
    優(yōu)質(zhì)解答
    sinx+siny+sinz-sin(x+y+z)=4sin[(x+y)/2]sin[(x+z)/2]sin[(y+z)/2]
    sinx+siny+sinz-sin(x+y+z)
    =2sin[(x+y)/2]cos[(x-y)/2]+sinz-sin(x+y)cosz-sinzcos(x+y)
    =2sin[(x+y)/2]cos[(x-y)/2]+sinz[1-cos(x+y)]-sin(x+y)cosz
    =2sin[(x+y)/2]cos[(x-y)/2]+2sinz*sin[(x+y)/2]^2-2sin[(x+y)/2]cos[(x+y)/2]cosz
    =2sin[(x+y)/2]*{cos[(x-y)/2]+sinzsin[(x+y)/2]-cos[(x+y)/2]cosz}
    =2sin[(x+y)/2]*{cos[(x-y)/2]-cos[z+(x+y)/2]}
    =2sin[(x+y)/2]*2sin[(x+z)/2]sin[(y+z)/2]
    =4sin[(x+y)/2]sin[(x+z)/2]sin[(y+z)/2]
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