>John,
>
>but I simply multiplied one equation by a, the other by b,
>and the third by c. It is pretty simple.

I suppose there are many simple ways to make the three equations into the Law of Cosines. I like what you did, just had a different view when I came up with the idea - especially when trying to think of how this might play out geometrically.

>I've been playing with the idea of using
>
>http://www.jsxgraph.org
>
>Do have a look. It is extremely simple. Practically no
>programming, only definitions of objects.

I am kind of iffy on how this thing works. There is a download but no .exe file or canvas to create the objects in. It seems as if you need to use GeoGebra or something to create the objects and then use this somehow to generate the embeddable code for what you created elsewhere. If I am wrong in this, please point me in the right direction.

Also, I have attached what the obtuse case might look like. It is a crude drawing I wrote on my whiteboard at school, but illustrates what I wrote in an earlier post...

https://docs.google.com/viewer?a=v&pid=explorer&chrome=true&srcid=0Bwc0zPMWJ9wqZDBmZmZhNjUtZjE2Mi00ZWQxLWIyN2YtOGI2MzhiNDgyYmM3&hl=en&authkey=CP_JvtYB