Đk $x\ge-1$
$\Leftrightarrow \sqrt{x^4+1}-\sqrt{x^3+1}+\sqrt{x^2+1}-\sqrt{x+1}=0$$\Leftrightarrow \frac{x^4-x^3}{\sqrt{x^4+1}+\sqrt{x^3+1}}+\frac{x^2-x}{\sqrt{x^2+1}+\sqrt{x+1}}=0$
$\Leftrightarrow \left[ {\begin{matrix} x^2-x=0\\ \frac{x^2}{\sqrt{x^4+1}+\sqrt{x^3+1}}+\frac1{\sqrt{x^2+1}+\sqrt{x+1}}=0(vônghiệm) \end{matrix}} \right.$
$\Leftrightarrow \left[ {\begin{matrix} x=0(tm)\\ x=1(tm)\end{matrix}} \right.$