[tex]x-2\sqrt{x}-3=0\\-2\sqrt{x} =-x+3\\(-2\sqrt{x})^2=(-x+3)^2\\4x=x^2-6x+9\\10x-9-x^2=0\\x^2-10x+9=0\\x^2-x-9x+9=0\\x(x-1)-9(x-1)=0\\(x-1)(x-9)=0\\x_{1} =1.\\x_{2} =9.[/tex]

Проверка:

[tex]1-2\sqrt{1} -3=0 = > x\neq 1.\\9-2\sqrt{9} -3=0 = > x=9.\\\\\\x=9.\\[/tex]

Ответ: Г.