\(B=\dfrac{2x^2+4}{2x^2+1}\)
\(B\in Z\Rightarrow2x^2+1+3⋮2x^2+1\)
\(2x^2+1⋮2x^2+1\Rightarrow3⋮2x^2+1\)
\(\Rightarrow2x^2+1\in U\left(3\right)\)
\(U\left(3\right)=\left\{\pm1;\pm3\right\}\)
mà \(2x^2+1\ge0\) nên:
\(\left\{{}\begin{matrix}2x^2+1=1\Rightarrow2x^2=0\Rightarrow x^2=0\Rightarrow x=0\left(TM\right)\\2x^2+1=3\Rightarrow2x^2=2\Rightarrow x^2=1\Rightarrow x=\pm1\left(TM\right)\end{matrix}\right.\)
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