3

I want to make a system with two equations but with biggest numbers, because now I can't see the number in the paper and my teacher will not see well. The system is:

\documentclass{article}
\usepackage[top=2cm, bottom=2cm, left=2cm, right=2cm]{geometry}
\usepackage{amstext}
\begin{document}
$$\left\{    
\begin{matrix}
I_1=I_2+I_3+I_4\\
I_3=I_5+I_6\\
\end{matrix}\right.
\Leftrightarrow
\left\{
\begin{matrix}
\frac{5-u_A}{1\times10^3}=\frac{u_A-4}{2,2\times 10^3}+
\frac{u_A-u_B}{4,7\times 10^3}+\frac{u_A}{4,5\times 10^3}\\
\frac{u_A-u_B}{4,7\times 10^3}=\frac{u_B}{6,8\times10^3}+2\times10^3
\end{matrix}\right.$$
\end{document}
Carmen González
  • 741

1 Answers1

8

Something like this? Note the use of (a) the array package and array environments, (b) the use of (typographic) struts so that the rows in the first array line up with the ones in the second array, (c) curly braces to encase the commas that serve as decimal markers and (d) \addlinespace to provide a bit more whitespace between the rows.

enter image description here

\documentclass{article}
\usepackage{array,amssymb,booktabs}
\newcommand{\tallstrut}{\vphantom{\frac{5_A}{4,10^3}}} % a typographic strut

\begin{document}
\[
\left\{
\begin{array}{>{\displaystyle\tallstrut}l@{}}
I_1=I_2+I_3+I_4\\ 
\addlinespace
I_3=I_5+I_6
\end{array}
\right.
\Leftrightarrow
\left\{
\begin{array}{>{\displaystyle}l@{}}
\frac{5-u_A}{1{,}0\times10^3}=\frac{u_A-4}{2{,}2\times 10^3}+
\frac{u_A-u_B}{4{,}7\times 10^3}+\frac{u_A}{4{,}5\times 10^3}\\ \addlinespace
\frac{u_A-u_B}{4,7\times 10^3}=\frac{u_B}{6{,}8\times10^3}+2\times10^3
\end{array}
\right.
\]

\end{document}

Addendum: As @egreg has noted in a comment, the same output may be achieved -- with slightly less typing -- by employing dcases environments (provided by the mathtools package):

\documentclass{article}
\usepackage{amssymb,booktabs,mathtools}
\newcommand{\tallstrut}{\vphantom{\frac{5_A}{4,10^3}}} % a typographic strut

\begin{document}

\[
\begin{dcases}
I_1=I_2+I_3+I_4\tallstrut\\
\addlinespace
I_3=I_5+I_6\tallstrut
\end{dcases}
\Leftrightarrow
\begin{dcases}
\frac{5-u_A}{1{,}0\times10^3}=\frac{u_A-4}{2{,}2\times 10^3}+
\frac{u_A-u_B}{4{,}7\times 10^3}+\frac{u_A}{4{,}5\times 10^3}\\ \addlinespace
\frac{u_A-u_B}{4,7\times 10^3}=\frac{u_B}{6{,}8\times10^3}+2\times10^3
\end{dcases}
\]

\end{document}
Mico
  • 506,678