documentclass[border=3pt]{standalone}
usepackage{tikz}
begin{document}
begin{tikzpicture}
draw[-,fill=white!95!red](0,0)--(3,0)--(4,1)--(1,1)--cycle;
node at (2,0.5) {$|textcolor{blue}{a}times textcolor{red}{b}|$};
draw[ultra thick,-latex,blue](0,0)--(3,0)node[midway,below]{$a$};
draw[ultra thick,-latex,red](0,0)--(1,1)node[midway,above]{$b$};
draw[ultra thick,-latex,blue!50!red](0,0)--(0,3)node[pos=0.7,right]{$atimes b$};
draw (0.6,0) arc [start angle=0,end angle=45,radius=0.6]
node[pos=0.7,right]{$theta$};
end{tikzpicture}
end{document}