作业帮一道简单的三角比证明题求证：4sin[(b-c)/2]sin[(a-b)/2]sin[(c-a)/2]=sin(b-c)+sin(a-b)+sin(c-a)sin2x(cos2y-1)+sin2y(cos2x-1) =-2sin2x(siny)^2-2sin2y(sinx)^2有一个负号啊~但是另一边化简出来没有负号，难道cos2y=2(siny)^2+
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![一道简单的三角比证明题求证：4sin[(b-c)/2]sin[(a-b)/2]sin[(c-a)/2]=sin(b-c)+sin(a-b)+sin(c-a)sin2x(cos2y-1)+sin2y(cos2x-1) =-2sin2x(siny)^2-2sin2y(sinx)^2有一个负号啊~但是另一边化简出来没有负号，难道cos2y=2(siny)^2+](/uploads/image/z/12973075-43-5.jpg?t=%E4%B8%80%E9%81%93%E7%AE%80%E5%8D%95%E7%9A%84%E4%B8%89%E8%A7%92%E6%AF%94%E8%AF%81%E6%98%8E%E9%A2%98%E6%B1%82%E8%AF%81%EF%BC%9A4sin%5B%28b-c%29%2F2%5Dsin%5B%28a-b%29%2F2%5Dsin%5B%28c-a%29%2F2%5D%3Dsin%28b-c%29%2Bsin%28a-b%29%2Bsin%28c-a%29sin2x%28cos2y-1%29%2Bsin2y%28cos2x-1%29+%3D-2sin2x%28siny%29%5E2-2sin2y%28sinx%29%5E2%E6%9C%89%E4%B8%80%E4%B8%AA%E8%B4%9F%E5%8F%B7%E5%95%8A%7E%E4%BD%86%E6%98%AF%E5%8F%A6%E4%B8%80%E8%BE%B9%E5%8C%96%E7%AE%80%E5%87%BA%E6%9D%A5%E6%B2%A1%E6%9C%89%E8%B4%9F%E5%8F%B7%EF%BC%8C%E9%9A%BE%E9%81%93cos2y%3D2%28siny%29%5E2%2B)
一道简单的三角比证明题求证：4sin[(b-c)/2]sin[(a-b)/2]sin[(c-a)/2]=sin(b-c)+sin(a-b)+sin(c-a)sin2x(cos2y-1)+sin2y(cos2x-1) =-2sin2x(siny)^2-2sin2y(sinx)^2有一个负号啊~但是另一边化简出来没有负号，难道cos2y=2(siny)^2+
一道简单的三角比证明题
求证：4sin[(b-c)/2]sin[(a-b)/2]sin[(c-a)/2]=sin(b-c)+sin(a-b)+sin(c-a)
sin2x(cos2y-1)+sin2y(cos2x-1)
=-2sin2x(siny)^2-2sin2y(sinx)^2
有一个负号啊~但是另一边化简出来没有负号，难道
cos2y=2(siny)^2+1?是cos2y=-2(siny)^2+1
一道简单的三角比证明题求证：4sin[(b-c)/2]sin[(a-b)/2]sin[(c-a)/2]=sin(b-c)+sin(a-b)+sin(c-a)sin2x(cos2y-1)+sin2y(cos2x-1) =-2sin2x(siny)^2-2sin2y(sinx)^2有一个负号啊~但是另一边化简出来没有负号，难道cos2y=2(siny)^2+
令(b-c)/2=x (a-b)/2=y
则x+y=(a-c)/2 (c-a)/2=-x-y
4sin[(b-c)/2]sin[(a-b)/2]sin[(c-a)/2]=sin(b-c)+sin(a-b)+sin(c-a)
即4sinxsinysin(-x-y)=sin2x+sin2y+sin(-2x-2y)
4sinxsinysin(x+y)=sin(2x+2y)-sin2x-sin2y
sin(2x+2y)-sin2x-sin2y
=sin2xcos2y+cos2xsin2y-sin2x-sin2y
=sin2x(cos2y-1)+sin2y(cos2x-1)
=-2sin2x(siny)^2-2sin2y(sinx)^2
4sinxsinysin(x+y)
=4sinxsiny(sinxcosy+cosxsiny)
=4(sinx)^2sinycosy+4(siny)^2sinxcosx
=2(sinx)^2sin2y+2(siny)^2sin2x
sin(2x+2y)-sin2x-sin2y=-4sinxsinysin(x+y)
a,b,c之间应该有关系吧？