Đặt \(\left|3x-1\right|=b\left(b\ge0\right)\)
\(\Rightarrow B=b^2-4b+5=\left(b-2\right)^2+1\ge1\)
Dấu "=" xảy ra khi \(b-2=0\)
\(\Rightarrow\left|3x-1\right|=2\)
\(\Rightarrow\left[{}\begin{matrix}3x-1=2\\3x-1=-2\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=1\\x=-\dfrac{1}{3}\end{matrix}\right.\)
Vậy Min B = 1 khi x = 1 hoặc x = - 1/3