^.$$\documentclass[00pt]{minimal}                 \usepackage{amsmath}                 \usepackage{wasysym}                  \usepackage{amsfonts}                  \usepackage{amssymb}                  \usepackage{amsbsy}                 \usepackage{mathrsfs}                 \usepackage{upgreek}                 \setlength{\oddsidemargin}{-00pt}                 \begin{document}$$ D_{R} (t) = D_{R} (\infty ) + \left[ {D_{R} (0) - D_{R} (\infty )} \right] \cdot e^{{ - k_{\text{dis}} t}} 