## Cubic Regression

The cubic regression option finds the equation of a cubic equation of
the form y = ax^{3} + bx^{2} + cx + d 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 cubic equation for this data is approximately
y = -.00698x^{3} - .0859x^{2} + 6.17x - 5.67.
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 cubic equation is an exact fit if four noncollinear, nonparabolic data points
are entered.
The TI-86 does not calculate the correlation coefficient r.