So which line
is the REAL "lineofbestfit"? 
In the lesson on
Line of Best Fit (without the graphing calculator), we discovered
that finding the lineofbestfit may lead to many "different" equations
depending upon the points chosen to construct the line.
Simply stated, the graphing calculator
has the capability of determining which line will actually represent the
REAL lineofbestfit.

The directions on this page were
prepared using
the TI83+/TI84+ graphing calculator.
Use
of the graphing calculator will help you to
better
understand the concept of line of best fit.



Let's examine
our fast food problem again with the use of the graphing calculator.
(This example and chart
are from MathBits.com and were used with permission.)
Is there a
relationship between the fat grams
and the total calories in fast food?

Sandwich 
Total Fat (g) 
Total Calories 
Hamburger 
9 
260 
Cheeseburger 
13 
320 
Quarter Pounder 
21 
420 
Quarter Pounder with Cheese 
30 
530 
Big Mac 
31 
560 
Arch Sandwich Special 
31 
550 
Arch Special with Bacon 
34 
590 
Crispy Chicken 
25 
500 
Fish Fillet 
28 
560 
Grilled Chicken 
20 
440 
Grilled Chicken Light 
5 
300 

Can we predict the number of
total calories based upon the total fat grams?

1. Enter the data in the calculator
lists. Place the data in L_{1} and L_{2}.
STAT, #1Edit, type values into the lists 

2.
Prepare a scatter plot of the data.
Set up for the scatterplot.
2^{nd} StatPlot  choices shown at
right.
Choose ZOOM #9 ZoomStat. Graph shown below.


3.
Have the calculator determine the line of
best fit.
STAT → CALC #4 LinReg(ax+b)
Include the parameters L_{1},
L_{2}, Y_{1}.
(Y_{1} comes from
VARS → YVARS, #Function, Y_{1})
You now have the values of a and b needed to
write the equation of the line of best fit. See values at
the right.
y = 11.73128088x + 193.8521475


4. Graph
the line of best fit.
Simply hit GRAPH.
To get a predicted value within the
window, hit TRACE, up arrow, and type the desired value.

Question: Predict the total
calories based upon 22 grams of fat.
ANS:
451.940 calories 
