Logarithmic Regression
The logarithmic regression option finds the equation of a logarithmic equation of
the form y = a + b ln x that best fits a set of data.
First, press 
to
enter the data .
The values of x must, of course, be greater than zero.
The data shown here is the points {(2,11.4) (3,17) (5,27.3) (7,36.1) (11,47.7) (13,49.9)}.
Press 
to view the statistics calculation options.
Press 
.
Therefore, the best-fit logarithmic equation for this data is approximately y = - 5.45 + 21.5 ln x.
The regression equation can be automatically stored in the equation editor
by pressing 
then typing the name of the equation, such as y1, and pressing .
Note: The TI-85 calculates the correlation coefficient, r, as corr.