When I try to find Intercept on my graph I : [2nd]Trace [Enter] (for first curve) [Enter] (for second curve) but nothing happens. It still asks me for second curve. I move the point to diffrent locations and [Enter] but still asks me for second curve. What am I doing wrong?

Here you are trying to find the intersection point between two curves. Since you could have drawn more than 2 curves, the calculator gives you the opportunity to choose the first curve using the arrow Up/ arrow down to select.

Once the curves are chosen, the calculator wants to know where (in the world is Carmen Sandiego) is the intersection point. And no it is not asking you to give the position, just what are the leftmost (1st guess) and rightmost (2nd guess) limits of the interval where the intersection point is. You use the left arrow to go a bit to the left of the intersection point (which you see on the graph) and press ENTER. Then you do the same for the 2nd guess.

Here you are trying to find the intersection point between two curves. Since you could have drawn more than 2 curves, the calculator gives you the opportunity to choose the first curve using the arrow Up/ arrow down to select.

Once the curves are chosen, the calculator wants to know where (in the world is Carmen Sandiego) is the intersection point. And no it is not asking you to give the position, just what are the leftmost (1st guess) and rightmost (2nd guess) limits of the interval where the intersection point is. You use the left arrow to go a bit to the left of the intersection point (which you see on the graph) and press ENTER. Then you do the same for the 2nd guess.

To find the intersection (read interSECTION) of two curves you are prompted once for an initial guess. If the calculator does not find the intersection point , or if there are more than one intersection points, you have to restart the procedure.
For your information, the interCEPT (or y-intercept) is the ordinate of the point where a curve cuts the y-axis. It is easy to mistake one word for the other. They are not synonymous.

The first curve is taken to be the one in Y1= equation. To select the 2nd curve (or to jump from one curve to the next) you use the Up Arrow or the Down Arrow. The left and right arrows allow you to move along a single curve (trace).

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 (L3,L4, etc.)

DRAWING THE SCATTER PLOT

Now you can press the [GRAPH] function key. 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 to select the 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 explicitly on the command line. Just press [2nd][L1] then [2nd] [L2] to get the following screen

Pressing [ENTER] to execute the command will get you the regression equation 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 of the OS (version 2.53MP) you press [MODE], scroll down to get to the second page of options and selected Stat Diagnostics ON


Thus to be able to draw the 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

After you press ENTER you obtain the equation, a,b,c, and R2. By pressing the [GRAPH] function key you get the raw data and the regression on the same screen.


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 move along the 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

Your question is a very interesting one and I believe people will benefit from a complete solution to it. So I will provide a solution but I will apply it to a quadratic regression.
The points I will represent are those on a parabola
L1= {0,1,2,3,4,5,6,7,8,9,10}
L2={0,1,4,9,16,25,36,49,64,81,100}
As you can see, I am cheating (no experimental points will fit a perfect parabola) but this will have no incidence on what I am going to show you.

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 (L3,L4, etc.)

DRAWING THE SCATTER PLOT

Now you can press the [GRAPH] function key. 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 to select the 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 explicitely on the command line. Just press [2nd][L1] then [2nd] [L2] to get the following screen

Pressing [ENTER] to execute the command will get you the regression equation 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 catalaog, or as in the newer version of the OS (version 2.53MP) you press [MODE], scroll down to get to the second page of options and selected Stat Diagnostics ON


Thus to be able to draw the 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

After you press ENTER you obtain the equation, a,b,c, and R2. By pressing the [GRAPH] function key you get the raw data and the regression on the same screen.


As you can see both are represented

TRACING THE REGRESSION CURVE (Sorry it took so long to arrive to the point)
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 move along the 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

I believe I already showed you with a profusion of details how to graph functions on the calculator. It would very kind of you to refer to the post that answered your question, so as not to make us answer it all over again. Much appreciated.

Read the following to use the intersection function.

1. You draw two or more graphs.
2. After the graphs are displayed, press [2nd][TRACE] to access the (CALC)ulate menu.
   
3. Select [5:Interesct]
4. You will be prompted for a first curve: the equation of the curve will be displayed at the top left corner of the screen. If it is one the intersecting curves, press [ENTER]
5. You will be prompted for the second curve. (You can move from one curve to another by pressing the UpArrow or DownArrow).
6. After two curves are selected, you will be prompted for a guess for the X-value of an intersection point: you can use the keypad to enter a guess or use the left or right arrow to move the cursor towards a point of your choosing (if there are more than one point).
7. After a short while the calculator gives you a solution.
8. If it fails, you must make a better guess.
   

Here are some screen captures

1. You draw two or more graphs.
2. After the graphs are displayed, press [2nd][TRACE] to access the (CALC)ulate menu.
   
3. Select [5:Interesct]
4. You will be prompted for a first curve: the equation of the curve will be displayed at the top left corner of the screen. If it is one the intersecting curves, press [ENTER]
5. You will be prompted for the second curve. (You can move from one curve to another by pressing the UpArrow or DownArrow).
6. After two curves are selected, you will be prompted for a guess for the X-value of an intersection point: you can use the keypad to enter a guess or use the left or right arrow to move the cursor towards a point of your choosing (if there are more than one point).
7. After a short while the calculator gives you a solution.
8. If it fails, you must make a better guess.
   

Graph the function then use the trace function to locate the point(s) where two curves intersect. In your case one of the curves is the X-AXIS.

See the screen capture to learn how to use the trace functionality.

Hello,
The function Intersect from the CALCULATE menu finf the coordinates of a point at which two or more curves intersect.
To use it:
1. Draw the functions.

2. Press [2nd][CALC][5:Intersect]



The cursor is on one of the curves. Read the equation top of the screen. If it is one of the curves you want press [ENTER]. The cursor jumps to another curve (in this case the only other curve).

Read the equation on top of the screen to verify thst it is the correct one. Press [ENTER]. The calculator asks asks for a guess of the coordinates of the intersection point.


As the intersection point is to the left of the current cursor position, use the left arrow to move cursor closer to the point.


Press [ENTER], and wait for the solution. Here it is.


In your question you talk about y intercept. If you want to calculate the ordinate of the point where a curve intersects the Y-axis, it is more efficient to use the [2nd][CAL][1:Value] selection.

You enter X=0 and press [ENTER]. The cursor jumps on the first curve (Y1=) an gives you the y-intercept.

Notice the position of cursor on graph. The y-value at the bottom is its ordinate.
To get the y-intercept of the second curve, leave the cursor on y axis and press the DownArrow. Cursor jumps to tthe second curve.
Since the X=0 is still stored, the value of y is displayed directly.



Hope it helps.