[tex] \sqrt{x - 4} = \dfrac{x}{4} [/tex]
[tex] (\sqrt{x - 4} )^2 = ( \dfrac{x}{4} )^2[/tex]
[tex]x - 4 = \dfrac{x^2}{16}[/tex]
[tex]16(x - 4) = x^2[/tex]
[tex]16x - 64 = x^2[/tex]
[tex]x^2 - 16x + 64 = 0[/tex]
[tex](x - 8)^2 = 0[/tex]
[tex]x - 8 = 0[/tex]
[tex]\bf x = 8[/tex]
