\documentclass{article}
\usepackage[margin=1in]{geometry}
\usepackage{amsmath}
\usepackage{tikz}
\usepackage{tkz-euclide}

\begin{document}
\begin{tikzpicture}
  \tkzDefPoints{0/0/A,4/0/B,3/2/C}
  \tkzDrawPoints{A,B,C}
  \tkzDrawPolygon(A,B,C)
  \tkzLabelSegment(A,C){$\sqrt{13}$}
  \tkzMarkAngle[size=.5cm](A,B,C)%
  \tkzLabelAngle[pos=1](C,B,A){$26.6^\circ$}%
\end{tikzpicture}
\end{document}