Quartic Regression
The quartic regression option finds the equation of a cubic equation of
the form y = ax4 + bx3 + cx2 + dx + e
that best fits a set of data.
First, press 
to
enter the data .
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 linear equation for this data is approximately
y = .00011x4 - .0104x3 - .0504x2 + 6.037x - 3.89.
(Note the scientific notation for the first term.)
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 resulting quartic equation is an exact fit if five noncollinear, nonparabolic,
noncubic data points are entered.
The TI-85 does not calculate the correlation coefficient r.