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, enter
the data . Press .
to select CALC.
Therefore, the best-fit quartic equation for this data is approximately
y = -0.69x4 + 8.99x3 - 43.2x2 + 90.8x
- 61.1. The TI-83 stores the regression equation. The equation can be graphed
and is transfered to
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 quartic equation is an exact fit if five noncollinear,
nonparabolic, noncubic data points are entered.
The TI-83 does not calculate the correlation coefficient r but does
calculate the coefficient of determination r2. Press
to see it.
The value here of .99898 indicates a very good fit.