Math Help - [SOLVED] Boundary conditions

1. [SOLVED] Boundary conditions

Hi
I have the heat equation

$\frac{\partial u}{\partial \tau}=\frac{\partial^2 u}{\partial x^2}$

where -infinity< x <infinity
and tau>0

with u(x,0)=H(x) the heavyside function

and I'm looking for a solution of the form u(x, tau)=U(y) where y=x/sqrt of tau.

How do the boundary conditions become
U(-infinity)=0
and
U(infinity)=0

I did something and got 1/0!! maybe limits are needed? Thanks for any help

2. ok so my attempt at latex didnt work. any ideas why?