As I'm not from america, I'm not familiar with the IB extended essay. Can it be a mathematical text, or does it need to be an essay without formula's and derivations?
Anyways, there are some great topics out there:
- an essay on the set theoretic controversy in the beginning of this century, and how it lead to an entirely different axiomatic system for mathematics. And how it lead to the conclusion that logic is indispensable in mathematics.
- Godel's incompleteness theorem: write about it's consequences and it's philosophical ramifications.
- Diophantos equations and the last theorem of Fermat.
- Infinity in mathematics