Take a look at the applet: Logarithmic function
A function of the form is called a logarithmic function. In this function, and is a fixed given base.
The graphs of the functions en are mirror images of each other with respect to the line . They are inverse functions of each other.
You can therefore derive the characteristics of from those of :
the domain is ;
the range is ;
the graph is increasing while , and decreasing while ;
the -axis is the vertical asymptote of the graph.
All functions that can be derived from transformations of are called logarithmic functions.