Vertical Spacing inside theorem enviroment

Question

I am using theorem enviroment to seperate 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}

\linespread{1}
\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}

Answer 1

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}

will add the desired vertical space.