Vì \(2x^2\ge0\Rightarrow2x^2+1\ge1\Rightarrow\left(2x^2+1\right)^4\ge1\Rightarrow\left(2x^2+1\right)^4-3\ge-2\)
\(\Rightarrow B\ge-2\)
\(\Rightarrow MIN_B=-2\Leftrightarrow\left(2x^2+1\right)^4=1\Leftrightarrow2x^2+1=1\Leftrightarrow2x^2=0\Leftrightarrow x=0\)