Regression (TI 85)

Goal: We wish to determine a "closest" function of a given form to the points represented by a list of ordered pairs (the data points).

Preliminaries:We will proceed with an example that finds the best fit to our data points in the form of a 3rd degree polynomial.

Assume that the data is represented in two lists. The first list, L1, contains the x-coordinates (in order) of our data points and the second list, L2, contains the y-coordinates.

Step by step method:

• STAT/EDIT
• Enter L1 as an xlist name (clear old entry if needed) and enter L2 as a ylist name
• Pressing enter after the y-list entry gives an edit screen where you type in x1 and y1. Enter again to give an opportunity to type x2 and y2. Enter all list pairs. EXIT to home screen.
• STAT/CALC Then enter the list names
• After the 2nd list name the lower menu line shows regression choices. Select P3REG
• Produced, is a list named PRegC containing coefficients of the regression ploynomial listed from the coeff of x^3 downward
• To put the polynomial in y1, either enter the variable RegEq (from the STAT/VARS menu) or type PRegC(1)x^3+PRegC(2)x^2+PRegC(3)x+PRegC(4) after \y1= on the "Y=" screen.

Remark: Other function forms are available at the point where P3REG is chosen.

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