\documentclass[tikz]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.15}
\usepackage{mathrsfs}
\usetikzlibrary{arrows,calc}
\usepackage{tkz-euclide}
\pagestyle{empty}
\usepackage{fp}

\definecolor{AngleClr}{rgb}{0,0.39215686274509803,0}
\definecolor{ShapeClr}{rgb}{0.6,0.2,0}

\begin{document}

\begin{tikzpicture}[scale=.75]
\tkzSetUpLine[line width=1pt,color=black]
\tkzSetUpPoint[fill=black]

\tkzDefPoints{0/0/A,6/0/C,2/1.5/B,2/-4/D}

\tkzFillPolygon[fill=ShapeClr,fill opacity=0.1,inner sep=1cm](A,B,C,D)

% Find the intersection of the diagonals.
\tkzInterLL(B,D)(A,C) \tkzGetPoint{I}

\tkzMarkRightAngle[line width=0.5pt, size=.15,color=AngleClr,fill=AngleClr,fill opacity=0.1](B,I,C)

\tkzDrawSegment[line width=0.5pt,color=black](A,C)
\tkzDrawSegment[line width=0.5pt,color=black](B,D)

\tkzDrawPolygon[color=ShapeClr](A,B,C,D)
\tkzDrawPoints[size=3](A,B,C,D)
\tkzLabelPoint[left](A){$\mathrm{A}$}
\tkzLabelPoint[above](B){$\mathrm{B}$}
\tkzLabelPoint[right](C){$\mathrm{\Gamma}$}
\tkzLabelPoint[below](D){$\mathrm{\Delta}$}

\end{tikzpicture}

\end{document}