Answer:
0 < b < 1
Step-by-step explanation:
This is a logarithmic function [tex]f(x)=log_bx[/tex]
This is defined for all values of b greater than 0 (by nature) also x > 0
The function is increasing for values of b > 0
The function is decreasing for values of 0 < b < 1
Note: See attached graphs
