3) $x+1+\sqrt{x^{2}-4x+1} =3\sqrt{x} $$(x+1)+\sqrt{(x-1)^2-6x}=3\sqrt{x}$$1+\sqrt{1-6(\frac{\sqrt{x}}{x+1})^2}=3\left(\frac{\sqrt{x}}{x+1}\right)$Đặt $\frac{\sqrt{x}}{x+1}=a$ PT trở thành: $1+\sqrt{1-6a^2}=3a$$ ...................$
3)$x+1+\sqrt{x^{2}-4x+1} =3\sqrt{x} $$
\Leftrightarrow (x+1)+\sqrt{(x-1)^2-6x}=3\sqrt{x}$$
\Leftrightarrow 1+\sqrt{1-6(\frac{\sqrt{x}}{x+1})^2}=3(\frac{\sqrt{x}}{x+1})$Đặt $\frac{\sqrt{x}}{x+1}=a$
$\rightarrow $ PT trở thành: $1+\sqrt{1-6a^2}=3a$$
\rightarrow ...................$