documentclass{scrartcl}
usepackage{etex}
usepackage{amsmath}
usepackage{mathtools}
usepackage{cleveref}
usepackage{pgfplots}
usepackage{graphicx}
usepackage{wrapfig}
usepackage{fancyref}
usepackage{amssymb}
usepackage[utf8x]{inputenc}
usepackage{caption}
usepackage{subcaption}
usepackage{lipsum}
usepackage{blindtext}
usepackage{hyperref}
usepackage{floatrow}
usepackage{imakeidx}
addtokomafont{sectioning}{rmfamily}
usepackage{indentfirst}
makeindex

begin{equation}label{eq:funcao_dif}
v_1 = K v_i + frac{v_2}{Q} - v_3 = K v_i - frac{1}{sT}frac{1}{Q} v_1  +
frac{1}{sT} v_2 = K v_i - frac{1}{sT}frac{1}{Q} v_1  - frac{1}{s^2T^2}
v_1
end{equation}

{par A primeira parte é logo um circuito subtractor que simula a equação
ref{eq:funcao_dif}}