The cubic regression option finds the equation of a cubic equation of the
form y = ax3 + bx2 + cx + d that best fits a set
of data. First, enter
the data . Press .
to select CALC.
Therefore, the best-fit cubic equation for this data is approximately
y = 0.43x3 - 0.42x2 -1.1x -5.1. The TI-83 stores
the regression equation. The equation can be graphed and is transfered
without typing the equation as follows. Press
to select EQ.
to view the regression equation and press .
The equation is now entered in .
The data points can also be viewed. Access STAT PLOTS by pressing
to turn the plots on. Press .
Note: The resulting cubic equation is an exact fit if four noncollinear, nonparabolic
data points are entered.
The TI-83 does not calculate the correlation coefficient r but does
calculate the coefficient of determination r2. The value of
.999 indicates a very good fit.