Answer
The function f(x)=log9x is the logarithm function with base 9.
So f(9)=1
f(1)= 0
f(1/9)=-1
f(81)=2
f(3)=1/3
Work Step by Step
The answer must be the exponent that 9 is raised to in order to come to answer of x. For example f(81)=2 because 9 rasied to the second power will give you x=81.