## 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 .

Press to view the statistics calculation options.

Press

Enter the columns to be used for the x and y entries, c1 and c2
in this case. The regression equation can be automatically stored
in the equation editor by selecting the Stor RegEQ.

Therefore, the best-fit cubic equation for this data is approximately
y = 0.03x^{3} - 0.11x^{2} -0.89x -0.47.

**Note:** The resulting cubic equation is an exact fit if four non collinear,
non parabolic data points are entered.
The TI-89 does not calculate the correlation coefficient r. It
does calculate the coefficient of determination, r^{2}.