Homework Help: PDE- Harmonic Functions

1. Jul 7, 2012

Combinatorics

1. The problem statement, all variables and given/known data
Given a positive subharmonic function $u$ , defined on $R^2$, how can I prove that $u[ /itex] must be constant? 2. Relevant equations [itex] \Delta u \leq 0$ is the definition of subharmonic function !

3. The attempt at a solution
I've tried solving this by using a new function $v_\epsilon = u+ \epsilon log(\sqrt{x^2+y^2 } )$ , and then messing out with this $/epsilon$, but without any success.

Hope you'll be able to help !

Thanks !