Cubic Regression

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, 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 = -.00698x3 - .0859x2 + 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.