Em nghĩ là theo cái này@@
View attachment 29523
\[\\\sqrt{(x-1)(x^{2}+x+1)}=x^{2}+x+1+2(x-1) \\\Leftrightarrow \sqrt{\frac{x-1}{x^{2}+x+1}}=1+2.\frac{x-1}{x^{2}+x+1} \\Dat:\sqrt{\frac{x-1}{x^{2}+x+1}}=t(t\geq 0): \\t=1+2t^{2} \\\Leftrightarrow 2t^{2}-t+1=0\]
