[tex]DK:\left[\begin{array}{l} x\geq \frac{3+\sqrt{11}}{2}\\ \frac{-5}{4}\leq x\leq \frac{3-\sqrt{11}}{2} \end{array}\right.[/tex]
[tex]2x^2-6x-1-\sqrt{4x+5}=0\\\iff 2x^2-8x+2+2x-3-\sqrt{4x+5}=0\\\iff 2(x^2-4x+1)+\frac{4x^2-12x+9-4x-5}{2x-3+\sqrt{4x+5}}=0\\\iff (x^2-4x+1)(2+\frac{4}{2x-3+\sqrt{4x+5}})=0[/tex]
TH1: $x^2-4x+1=0 \iff ...$
TH2: [tex]2+\frac{4}{2x-3+\sqrt{4x+5}}=0\\\Leftrightarrow 4x-6+2\sqrt{4x+5}+4=0\\\Leftrightarrow \sqrt{4x+5}=1-2x\\\Leftrightarrow ...[/tex]