A Euler's circuit is a circuit, which goes over all edges in a graph once and only once. (Though i wonder why this was asked under calculus & analysis??)
A Google search can bring up lot more details on this one if you wish.
i asked my math teacher some question
1) Is space continuous?
2) The proof of least-square line
3) gauss' law and close intergral
4) the proof of some number theory questions
5) What is green's therom