If a cubic polynomial is a good fit for the data on a scatter plot, you need to perform a cubic regression. You can do this in the TI-Nspire Lists & Spreadsheets application. To perform a regression, follow these steps:

Press

**to move back to the Lists & Spreadsheet page containing the data needed.**Press [MENU]→Statistics→Stat Calculations→Cubic Regression.

A dialog box opens. As with any dialog box, you can press

**[TAB]**to move from one field to the next or**[SHIFT][TAB]**to move backward through the fields. Press**[ENTER]**at any time for the configuration to take effect.Notice in the first screen that pressing

**[CLICK]**and selecting*year*enables you to specify the location of the X List. You could also specify the column by its letter reference. In the second screen, pressing**[D][CTRL][ ( ]**enables you to indicate where you want the results to be stored. Column D because it is the first available empty column.The third and fourth screens (with columns D and E widened) show that the results of the regression are pasted directly into the spreadsheet. Notice that the

*coefficient of determination**,*R^{2}, is very close to 1. This might suggest that the choice of doing a cubic regression was a good one.

A cubic regression can be done with a minimum of four points. Under this scenario, TI-Nspire finds a third-degree polynomial fit by solving a system of four equations determined by using the *x*-* *and *y*-values of the four points. With five or more points, TI-Nspire performs a cubic regression.