We have recently recommenced work on our FX Library materials (which are designed to showcase the capabilities of our new MultiDocs technology) and started work on an interesting activity which we have decided to share early. As we were working on the activity, it proved to NOT be particularly suited to parametization but did develop in unexpected and interesting ways.
Semicircle Areas (Word document)

The activity is an interesting extension question for geometric series where students are asked to use their knowledge in an unusual way. If you are looking for an investigative activity for your higher-level students, this might be perfect!
As with all of our FX Library, the materials are provided with VERY generous copyright conditions. If you are using the activity in a school situation, you basically have free reign. Download away!