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\begin{eqnarray}[\{]
$$\frac{\partial{x_i}}{\partial{q_j}} = \sum_{j = 1}^{n}\frac{\partial{x_i}}{\partial{q_j}}  $$ \\
$$\frac{\partial{y_i}}{\partial{q_j}} = \sum_{j = 1}^{n}\frac{\partial{y_i}}{\partial{q_j}}  $$ \\
$$\frac{\partial{z_i}}{\partial{q_j}} = \sum_{j = 1}^{n}\frac{\partial{z_i}}{\partial{q_j}}  $$
\end{eqnarray}

I don't see the fault here. Could you guys please help me ??

4
  • Welcome to TeX SX! Even dolls can...
    – Bernard
    Feb 13, 2018 at 15:16
  • 3
    your use of eqnarray is very wrong ... remove all $ and than try again. if you will provide complete but small document we can easily show how to correct type your system of equations.
    – Zarko
    Feb 13, 2018 at 15:19
  • @Hitman01, anyway consider other part of my comment. eqnarray is considered obsolete. try to use environment from amsmath package.
    – Zarko
    Feb 13, 2018 at 15:36
  • @Hitman01: See eqnarray vs align.
    – Werner
    Feb 13, 2018 at 15:37

2 Answers 2

1

You shouldn't use eqnarray, as it leads to bad spacings. Use the amsmath environments instead. I suppose you're after this:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}

\usepackage{empheq}
\usepackage{esdiff}

\begin{document}

\begin{empheq}[left = \empheqlbrace\;]{align}
\diffp{x_i}{{q_j}} & = \smash[t]{\sum_{j = 1}^{n}}\diffp{x_i}{{q_j}} \\
\diffp{y_i}{{q_j}} & = \sum_{j = 1}^{n}\diffp{y_i}{{q_j}} \\
\diffp{z_i}{{q_j}} & = \smash[b]{\sum_{j = 1}^{n}}\diffp{z_i}{{q_j}}
\end{empheq}

\end{document} 

enter image description here

1

or with use cases package;

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}

\usepackage{cases}
\usepackage{esdiff}

\begin{document}

\begin{numcases}{}
\diffp{x_i}{{q_j}} = \sum_{j=1}^{n}\diffp{x_i}{{q_j}} \\
\diffp{y_i}{{q_j}} = \sum_{j=1}^{n}\diffp{y_i}{{q_j}} \\
\diffp{z_i}{{q_j}} = \sum_{j=1}^{n}\diffp{z_i}{{q_j}}
\end{numcases}

\end{document}

enter image description here

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