Respuesta :

[tex]3x^2-18x+23=3(x^2-6x)+23=3(x^2-6x+9-9)+23[/tex]
[tex]\quad=3((x-3)^2-9)+23=3(x-3)^2-27+23=3(x-3)^2-4[/tex]

The vertex is then [tex](3,-4)[/tex].