Quadratic Regression
The quadratic regression option finds the equation of a quadratic equation of
the form y = ax2 + bx + c that best fits a set of data.
First, press 
to
enter the data .
Press 
to view the statistics calculation options.
Press 
.
Enter the columns to be used for the x and y entries, c1 and c2 in this case.
The regression equation can be automatically stored in the equation editor by selecting
the Stor RegEQ.
Therefore, the best-fit quadratic equation for this data is approximately
y = - 0.049x2 + 0.47x - 1.44.
Note: The resulting quadratic equation is an exact fit if three noncollinear data points
are entered.
The TI-89 does not calculate the correlation coefficient r. It does calculate
the coefficient of determination, r2.