求x在R上时,函数y=sin(x)/(2-cosx)的值域,过程,谢谢!

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设tan(x/2)=t则sinx=2t/(1+t^2)cosx=(1-t^2)/(1+t^2)代入整理后 y=2t/(1+3t^2)3yt^2-2t+y=0t∈(-∞,+∞)△=4-4*3y*y=0-3^(-1/2)<=y<=3^(-1/2)