Respuesta :

Globule

Hi !

[tex]f(x) = \frac{4}{x - 9} [/tex]

[tex]x-9[/tex] must be different from 0.

[tex]x -9 \ne0 \\ x \ne9[/tex]

[tex] = = > \: D_f=\mathbb{R}-\{9\}[/tex]

Have a nice day ;)