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Geometry Expressions Newsletter
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Geometry Expressions NewsletterJuly 2012  
Geometry Expressions and Lua
Lua is the preferred programming language for the TI-Nspire, and Geometry Expressions supports it in two ways:
  1. You can export single expressions as pieces of Lua code, using Copy As / Source Code / Lua
  2. You can export an entire Lua app using File / Export / Lua App 

The Lua apps require version 3.2 of the Nspire OS.

Sample Lua apps are available as tns files here

How to...create a Lua App with Geometry Expressions
Creating a Lua App in Geometry Expressions is very similar to creating an HTML5 App.  You follow these steps

First create your model inside Geometry Expressions, bearing the following in mind:
  • Points which you want to be freely draggable should have coordinate constraints, with the coordinates specified as variables.
  • Points which should drag along a curve or line should be constrained using the point proportional constraint, and its value should be set as a variable.
  • Only symbolic measurements will be available for output.  
Now do File/Export/Lua App.
 
A dialog appears which lets you add a title, and lets you specify which variables are accessible to the user and in what form.

Your Lua app will be saved as a text file, but it will also be saved onto the clipboard.

The quickest way to see your app is to insert a Script Editor in your TI-nSpire Document, and Paste your app.  Now do Set Script from the script editor.  (Remember you need to have version 3.2 or above of the TI-nSpire OS).
Lua app

Problem of the Month
Given a (smooth enough) function y=f(x), let

A = (x , f(x)),
B = (x+h  , f(x+h))
C = (x-h , f(x-h))

What is the relationship between the radius of the circumcircle of triangle ABC and the radius of its 9-point circle as h tends to 0?

An interactive app which lets you play with this problem is here.
Electronic Book Bundle

 
10 Geometry Expressions eBooks are now available as a bundle for the recession-friendly price of $79.95
Bundle includes:
  1. The Tortoise and Achilles
  2. Calculus Explorations  
  3. The Farmer and the Mathematician
  4. Developing Geometry Proofs  
  5. 101 Symbolic Geometry Examples
  6. 101 Conic Sections Examples  
  7. Using Symbolic Geometry to Teach Secondary School Mathematics  
  8. Connecting Algebra and Geometry through Technology
  9. Function Transformations
  10. Exploring with Geometry Expressions 

Videos
See our YouTube channel for videos exploring features in Geometry Expressions.

Phil Todd's TechIgnite talk connects central pivot irrigation in Texas to Malfatti's Problem
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