Answer:
[tex]\{3\}[/tex]
Step-by-step explanation:
Strictly speaking, we need to know the point of [tex]f(x) = 3x[/tex] intersecting [tex]f(x) = 9[/tex]. In other words, we need to solve the equality:
[tex]3x = 9; \\ x = \frac{9}{3}; \\ x = 3[/tex]
Here it is.
