# How do I get LaTeX to put the infinity on top of the SUM symboL

1. Aug 30, 2008

### laura_a

I need to make a power series in LaTex that looks like this
$$u = \Sigma^{\infty}_{k=0} a_kx^k$$

But I wan the infinity on top of the sum and the k=0 on the bottom like normal setting out but I can't find out how to do it?
Hopefully someone from here can show me! Thanks

2. Aug 30, 2008

### HallsofIvy

Staff Emeritus
$$u= \sum_{k=0}^\infty a_kx^k$$