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# TI's BEST FIT

GOAL: To find "best fit" lines using the technology of the TI-83

MATERIALS

TI-83 calculators
Windows PC

PROCEDURE

1. Using the TI-83, choose Stat, Edit, then enter the data for one variable in List 1 and the other variable in List 2. If you need to delete old information from the lists, highlight, at the top, the list you want to empty, press clear and enter.
2. Set an appropriate window for your graph based on the range of the data. Choose ExprOn from the Format menu.
3. Choose StatPlot, Plot 1, ON and select the first type of graph. Make sure L1 is the Xlist and L2 is the Ylist. Choose squares to mark your graph.
4. Press Graph to see your scatterplot.
5. To get the equation of the "best fit" line (regression equation), choose Stat, Calc, LinReg (ax + b), enter. Note: a = slope; b = y-intercept
6. Clear all equations in Y = Choose Y = , Vars, Statistics, EQ, RegEQ, Enter.
This process will paste the regression equation into the Y = menu. Press Graph to see how the line fits.
7. Connect your calculator to the graph link on the computer and open the TI-83 link program.
8. With your scatterplot and equation showing on the calculator, choose Link, Get Screen, 300%, Print. Label the window your used on your printout.

Let's compare our results from yesterday with the TI-83.

Example: The total amount (in millions of dollars) spent by the government on mathematics research from 1985 through 1995 is shown in the table. Find the "best fit" line and write its equation. Predict the amount to be spent in 2000. To center your graph, let x = 0 correspond with 1985.

 year 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 amt \$91 \$118 \$128 \$130 \$151 \$184 \$185 \$205 \$212 \$240 \$245

The point for the average of the coordinates is (5, 171.72)

Another point on the line is (10,245)

slope = (245 - 171.72) / (10 - 5) = 14.7

equation is:

 y - 245 = 14.7(x - 10) y - 245 = 14.7x - 147 y = 14.7x + 98

WINDOW [-2, 15] by [-50, 300]

Using yesterday's data, printout results from your TI-83. How did your equations compare?

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