Vertical Spacing inside theorem environment

I am using theorem environment to separate different exercises assigned as homework. So my plan is to write exe's description, move a few lines below and then give my solution. I am using \vspace{3cm} but it's not working.My code is

\documentclass[a4paper,11pt]{article}

\usepackage[english,greek]{babel}
\usepackage[iso-8859-7]{inputenc}
\setcounter{secnumdepth}{3}
\usepackage{kerkis}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsfonts}
\usepackage{amsthm}
\usepackage{resizegather}%allows the automatically resizing of equation to line width, if     equation is too large
\usepackage{units}
\usepackage{array}
\usepackage{framed}
\usepackage{extarrows}
\usepackage{cancel}
\usepackage[pdftex]{graphicx}
\usepackage[margin=2.8cm]{geometry}

\newcommand{\sw}{\selectlanguage{english}}
\newcommand{\sq}{\selectlanguage{greek}}
\newcommand{\eng}[1]{\latintext#1\greektext}
\newcommand{\gre}[1]{\greektext\latintext#1}

\theoremstyle{definition}
\newtheorem{exe}{Άσκηση}

\begin{document}
\begin{exe}
\sw
Prove \textit{Thomson's theorem}: If a number of surfaces are fixed in position and a given     total charge is placed on each surface, then the electrostatic energy in the region bounded     by the surfaces is an absolute minimum when the charges are placed so that every surface is     an equipotential, as happens when they are conductors.\\ \sq
\vspace{3cm}
\noindent \textbf{Λύση:}μπλα μπλα μπλα

\end{exe}

\end{document}

• \par\vspace{3cm} will do that job, but there probably is an official way to do this. – Peter Grill Oct 30 '12 at 7:39
• It works!!! Thank you very much! What do you mean "official way"? – Thanos Oct 30 '12 at 7:47
• Just thought there might a built in command to control this spacing/formatting. – Peter Grill Oct 30 '12 at 16:22

Since no one else has posted a solution, I am assuming that there is not another command that allows one to set that spacing. So, adding a \par before the \vspace:
\par\vspace{3cm}