## Cubic Regression

The cubic regression option finds the equation of a cubic equation of
the form y = ax^{3} + bx^{2} + 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_x^{3}
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 = -.00698x^{3} - .0859x^{2} + 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, r^{2}.