Question about Texas Instruments TI-84 Plus Silver Edition Graphic Calculator

# How do i find the line of best fit on my TI-84 plus addition?

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Here is a complete solution that shows you how to find the equation for the best curve fitting, how to draw that equation on the same screen as the scatter plot and also how to do interpolation or the best fit curve. The post may seem long for an impatient reader but it leaves no stone unturned. Please DO READ it till the end.

The data points used are for a parabola (QuadReg) but you can easily adapt it

The points I will represent are those on a parabola (squares of all integer numbers from 0 to 10). Substitute your own values in L1 and L2

L1= {0,1,2,3,4,5,6,7,8,9,10}
L2={0,1,4,9,16,25,36,49,64,81,100}

1. PREPARE THE GRAPH FORMAT (you will see why latter)
With the calculator turned On, press [2nd][ZOOM] to access the (FORMAT) screen. Notice that RectGC is highlighted. It means that the coordinates are rectangular. IF the POLARGC had been highlighted and you had used the TRACE function the values of the coordinates of the points being traced would be in the form (R, theta), in other words polar coordinates.

2. ENTER THE DATA

Press STAT, then under the EDIT menu press [1:Edit]

to open the list editing screen. Enter the elements of the two lists

After you enter the data in L1 and L1, Press [2nd][Y=] to open the (STAT PLOT)

3. CONFIGURE THE STAT PLOT TYPE

Initially the Plot1 may be OFF. Make sure at the beginning that all Stat Plots are OFF. If necessary press [4:PlotsOff] execute the command in Main calculator screen and press [2nd][Y=1] to get back at the stat plot screen configuration below

Press 1:Plot1 Off to open the P1 configuration
The cursor will be blinking on On. If not use cursor to highlight ON and press [ENTER]. The cursor will move to second line (TYPE), on first icon. Since you want to do a scatter PLOT that is the one to choose. Highlight it and press ENTER then move cursor with Down arrow to move to Xlist
If your data is in L1 and L2 Xlist and Ylist will be already selected. If you have entered your data in some other lists, enter the proper lists (how do i find the - e825b96.jpg)

DRAWING THE SCATTER PLOT

Now you can press the [GRAPH] fuhow do i find the - 0d9dbd0.jpg Here is what you get

PERFORMING A REGRESSION

Because I chose it so, we will perform a quadratic regression QuadReg
To do so you press [STAT] and use right arrow how do i find the - b12881c.jpghe CALC(ulate) Menu. Type 5:QuadReg

Command echoes on Main screen as QuadReg with blinking cursor as above on the right.

If you press [ENTER] the calculator will assign L1 to X and L2 to Y by default. If that does not correspond to the problem, you had better change the names of the lists used by entering then explicihow do i find the - 30d1079.jpg command line. Just press [2nd][L1] then [2nd] [L2] to get the following screen

Pressing [ENTER] to execute the command will get you the how do i find the - 2757d7c.jpgequation and its coefficients but you will not be able to have it graphed on the scatter plot

The coefficient/factor of determination R2 is displayed if you ran the DiagnosticOn command from the catalog, or as in the newer version ofhow do i find the - e380d1f.jpgersion 2.53MP) you press [MODE], scroll down to get to the second page of options and selected Stat Diagnostics ON

Thus to be ablhow do i find the - 0b6bc57.jpghe regression curve on the scatter plot, you must save it to a function variable, Y1 for example. You do it with the following command line

As you can see both are represented

TRACING THE REGRESSION CURVE
Press Trace and see what you get

As you can see the trace defaults to the scatter plot P1, L1,L2 (see the top left). If you stay on that graph you will on ly trace the actual data points (raw data). The cursor will jump from one point to the next.
To trace the regression curve (the second curve) you must move cursor on it. To do so press the Up and Down arrows. Left and right arrows allow cursor to mhow do i find the - ad6b3c2.jpghe same curve.
Pressing Down Arrow you move to the regression curve. Notice the equation on the top left corner. The cursor can be displaced anywhere (depending on the resolution of the graph.

If you want Y for a particular value of X, just enter the value of X
Enter an X value. How about 5.55555?

Type in the value and press [ENTER] et voil

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