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 selecting option AEDIT 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 DREG to view the regression options.

For cubic regression, select opton 05Rg_x3 using followed by four

Press and select cubic regression in the calculation screen. Now press followed by .

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 entering the name of the equation, such as y1, after (L1,L2 as follows: choose option A and select y1 followed by .

Note: The resulting cubic equation is an exact fit if four noncollinear, nonparabolic data points are entered.

The Sharp does not calculate the correlation coefficient r, but it does calculate the coefficient of determination, r2.