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Dynamic Text Using TI-Nspire
This page extends the introduction, available in Creating Interactive Documents using TI-Nspire. It explicitly shows the construction of points and segments that appear and disappear according to a given condition. In this example, as a point D dragged around a circle coincides with a tangent point T, text will appear to that effect and the tangent segment will appear in bold.
On the page shown, I have constructed the incircle of triangle ABC (this triangle has been hidden), and a point D on the circle. When point D meets the tangent of side AC (where circle and triangle meet at point T), we want two things to happen: text to appear, saying that we have a tangent, and a bold segment AC to appear.
Our test will be when the distance between the two points is very small, so we use the distance formula between points D and T, whose coordinates have been shown - call these (dx, dy) and (tx, ty). The when statement (shown) will output 1 when the condition is met.
To make the text appear, we choose a place where we want this to happen: I have constructed a line perpendicular to the x-axis to serve as the x-coordinate, and have put the text "5" to serve as the y-coordinate on this line. I have also created a text product (qq*ww) and will multiply the output of the when statement (1) by the text "5" to get a value that will appear and disappear. I use Measurement Transfer to place this on the y-axis, Perpendicular from this y-point to meet our other perpendicular and Point of Intersection to get a point at (-8, 5) that appears and disappears - and says "You have a tangent!"
The disappearing segment is easy too: we put a point on top of point A which depends on the when statement: again multiply the output 1 by both x and y-coordinates of A, use Measurement Transfer to place these on the axes, Perpendicular to Intersect on top of point A. The construct a segment from this new point to C and make it bold. (NOTE: after getting the coordinates of point A I then hid the actual point so that it didn't get in the way creating the new one on top of it - later it will need to be shown again).
We begin by creating the disappearing text:
Next we create the disappearing bold segment:
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