First of all I'm not sure if this is the right section, so I apologise if it's not.

I was hoping that someone could help me out with the following question:

From a piece of wire 5000mm long, n pieces are cut, each piece being 10mm longer than the previous piece. Ui is the length of the ith piece and Si is the cumulative length of i pieces.

Express Un and Sn in terms of U1 and n.