\(B=\frac{x^2-2x+2007}{2007x^2}\)
\(\Leftrightarrow B.2007x^2=x^2-2x+2017\)
\(\Leftrightarrow x^2-B.2007x^2-2x+2017=0\)
\(\Leftrightarrow x^2\left(1-2007B\right)-2x+2017=0\)
\(\Delta=4-4\left(1-2007B\right)2007\ge0\)
\(\Rightarrow B\ge\frac{2006}{2007^2}\) Dấu "=" xảy ra \(\Leftrightarrow x=2007\)
Vậy \(B_{min}=\frac{2006}{2007^2}\) tại \(x=2007\)
\(\)