The quartic regression option finds the equation of a cubic equation of
the form y = ax^{4} + bx^{3} + cx^{2} + dx + e
that best fits a set of data. First, enter
the data . Press .

Press
and use
to select CALC.

Press .

Therefore, the best-fit quartic equation for this data is approximately
y = -0.69x^{4} + 8.99x^{3} - 43.2x^{2} + 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
and use
to select EQ.

Press
to view the regression equation and press .
The equation is now entered in .
Press .
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 r^{2}. Press
to see it.

The value here of .99898 indicates a very good fit.