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Geometry Expressions Newsletter
January 2013   
Euclid's Muse hosts TI-Nspire apps
Euclid's Muse is your place to find interactive math apps created with Geometry Expressions.

With Geometry Expressions version 3.1 SP2, we added the ability to export Lua apps for the TI-Nspire.

We've now added the ability to post the tns files for use with the TI-Nspire along with the Browser apps.

So you can experience the interactivity on your browser, then download the tns file for use in your TI-Nspire.

Have a look at these examples

How to... Use generic ngons
When you create a regular polygon with Geometry Expressions, you drag from the center of the polygon to one of its vertices.  You then need to enter the number of sides.

As with other values entered into Geometry Expressions, this can either be numeric or symbolic.

If you use a variable (n, say) you can set its numeric value in the Variables Panel.

As you'd expect, when you make a symbolic measurement from the drawing it is expressed in terms of n, and not its numeric value.

Problem of the Month
CAD is an arc of a parabola with vertex A and focus B.
FGHI is the control polygon of a cubic spline.

Can you locate points FGHI so that the spline is exactly the parabolic arc?
If so, where?

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

November's Problem's Solution:
A string of length L is pinned at points A and B. Point c is the location of a pen, constrained by the string so that |AC|+|BC| = L


The locus of C is, of course, an ellipse with foci A and B and major axis L.

What is the locus of point D, the incenter of the triangle ABC?

In Geometry Expressions you can generate the locus, and derive its implicit equation.  As the equation is second order in X and Y, we can infer that the locus is a conic, and in fact an ellipse.

The locus passes through the foci of the original ellipse.  One principal axis is therefore easy, what is the other?
ellipse solution
on the Web

Slides from Prof. Dr. Heinz Schumann's presentation on algebraic computation from geometric figures (in German).

A Geometry Expressions generated app featured in an article on the Davidson Institute's site (now in English)

A collection of whimsical clocks with a mathematical falvor.

Pythagoras proof
Our  Euclid's Elements contains over 120 interactive diagrams.
Available on iTunes

Sample chapters of other iPad eBooks are available here.

Interactive math Apps which can be viewed on your iPad are available from Euclid's Muse

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

Watch more videos about creating Apps with Geometry Expressions.

Learn how to Export an Animation with Geometry Expressions.
Quick Links
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