The code below produces the mistake in the picture. Any idea why?
% !TEX encoding = UTF-8 Unicode\documentclass[a4paper,12pt]{report}\usepackage[utf8]{inputenc}\usepackage[T1]{fontenc}\usepackage{datetime}\usepackage[turkish]{babel}\usepackage{amsmath}\usepackage{amssymb}\begin{document}\begin{bmatrix}a & b \\c & d\end{bmatrix}\end{document} 
