f(x)=3x/(x^2+x+1)=3x/[(x-1/2)^2+3/4]x＞0时,f(x)＞0令f(x)=3x/(x^2+x+1)=mmx^2+(m-3)x+m=0判别式=(m-3)^2-4m*m≥03m^2+6m-9≤0(m+3)(m-1)≤0-3≤m≤1,即：-3≤f(x)≤1又：f(x)＞0,所以：0＜f(x)≤1值域（0,1] 【备...