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Create Your Own TI-Nspire Dynamic Number Line
This is a great place to get started with creating interactive documents using TI-Nspire. Use a scatterplot to create a useful number line template that can be applied to lots of different situations. Then step-by-step make it increasingly interactive. The magic happens in a Notes window which accompanies the graph window that houses the number line.
Step 1: Set up your document
Begin a new document. Use Doc > Page Layout > Select Layout > Layout 3 to split the page horizontally. Make the top window a Graph window and the bottom window a Notes app.
Click in the Notes app and Insert a MathBox. Use either menu > Insert > Math Box or simply press ctrl-m.
In the MathBox, type xlist := seq(i,i,-10,10). This defines a list of numbers from -10 to 10 and stores it as xlist.
When you press enter to activate the MathBox, two things will happen. You will see your list appear (in green!) and a new MathBox will open on the next line. Type ylist := seq(0,i,-10,10) to create a list of zeros of the same dimension as our list. These provide the basis for a scatterplot in the Graph page. Delete the additional empty MathBox that was auto-created after pressing enter a second time.
If you don't need your number line to be dynamic - you just need a quick number line - use a Calculator window to define your xlist and ylist as described above, then press ctrl-k and delete to throw the Calculator page away. Then just perform the next steps to create your scatterplot, quickly and easily!
Step 2: Set up your scatterplot
Either from menu > Graph Type > Scatter Plot or by right-clicking in the Function Entry line (the right-click on a handheld is ctrl-menu choose the ScatterPlot as our graph type.
Enter xlist for x and ylist for y and press enter to define our scatterplot.
Now right-click on the scatterplot and choose Attributes (or choose menu > Actions > Attributes and click on the scatterplot. Use your cursor arrows whether you are on computer or handheld and arrow right until you reach option 6/9 to turn the points into crosses. Then arrow down one step and right one step to connect your points. Congratulations, you have a number line! (although it may be a little hard to see while the axes are still visible behind - we need them for just a little longer yet!)
Step 3: Making it Dynamic!
Right-click on the minimum x-value of your x-axis (the number at the far left center of the window) and Store it as xmin (When you hover over the number - probably -10) it will say "Text". Choose 5. Store, type "xmin" and press enter); do the same, for the maximum x-value, storing it as xmax.
The next few steps are cosmetic but important if we want our number line to actually look like a number line. First, choose menu > View > Hide Axes. Right click on the chevron in the bottom left corner of the Graph page and choose option 3: Hide chevron. Finally, right-click on the label for the scatter plot (that says (xlist, ylist) and choose Hide.
Back in the Graph window, add a slider named xmin and another named xmax by choosing menu > Actions > Insert Slider. Drop the first in the top left corner by clicking there; immediately type the name (xmin) and press enter. Place the second slider in the top right corner and name it. Click in the lower bound of each and change these from 0 to -10. Then right-click on each and choose Minimize.
Finally, back to the Notes window and change the limits for the two sequences from -10 to 10 to min to xmax. Press enter after each and then go back and change your slider values to see your dynamic number line at work.
It would be even better if we could change the step size (or tick marks) on our number line. Insert a third slider and place it between the top two, or at the bottom centre of the window. Call it steps and set it to run from 1 to 10. Minimize it as before. Then in your sequence definitions, add a final additional argument:
xlist := seq(i, i, xmin, xmax, 1/steps)
ylist := seq(0, i, xmin, xmax, 1/steps)
Step 4: Finishing Touches
All done! The next steps are designed to protect your MathBoxes from student interference. Click in front of the xlist definition box and press enter a few times to push it down the page. Arrow back up to the first (empty) line of your Notes window. Then grab the horizontal dividing line between the two windows (or choose Doc > Page Layout > Custom Split and arrow down until it is as far down as it will go. Press enter to lock it there, and then click back in the Graph window.
To label the number line we need to be careful. Simply putting points on the scatterplot will not work because as soon as you change the xmin and xmax values, the relative positions of these points will change. One that will not change is the origin. Select menu > Geometry > Points & Lines > Point and type an opening parenthesis: "(". Now type 0 and press enter. Type 0 again and press enter. Use right-click to Pin that point.
A little Geometry is now required. Suppose we wish labels at each integer value on our number line. Right-click on any white space on the Graph page and insert a Text Box. Type "1" and press enter. From the Geometry menu, choose Shapes > Circle, click on the number 1 that you just created to set the radius, and then on your origin point. You have a circle, radius 1, center the origin. Choose Geometry > Points & Lines > Intersection Point(s), click on the circle and then on the x-axis to display the points at (1, 0) and (-1, 0).
Now we use a little Symmetry - choose menu > Geometry > Transformations > Symmetry. Click on the point at (1, 0), and then on the origin point - you will get a symmetrical point at (2, 0). Repeat this by clicking on the new point (2, 0) and then on the point (1, 0) to create a point at (3, 0). Continue for as many positive values as you care to label. Then do this for the negative values - click first on (-1, 0) and then on (0, 0) to produce (-2, 0), and so on.
Label these points by right-clicking and choose label (if you explore the Symbols Palette you will find the numbers from 0 to 9 and + and - available as superscripts and subscripts - either of these make great labels. If you wish to add labels to more points, I would suggest using menu > Constructions > Midpoint. Finally carefully place these labels in their correct positions (try to grab above the label to drag it) and then Pin then into position.
And you are done!
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