\documentclass[tikz]{standalone}
\usepackage{tikz}
\usepackage{tkz-euclide}

\begin{document}
\begin{tikzpicture}
    \tkzInit[xmax=5,ymax=5,xmin=-5,ymin=-5]
    \tkzGrid
    \tkzAxeXY
    \draw[thick, latex-latex] (-1,4) -- (4,-6) node[anchor=south west] {$a$};
\end{tikzpicture}
\end{document}