I have now the version
and want to change it to something like
The equations are in eqnarray and I want to underline only the last line. Is this possible?
[Tex/LaTex] Underline inside eqnarray
equations
Related Solutions
The \shoveleft and \shoveright commands allow to flush left or right the equations of a multline environment.
\documentclass{article}
\usepackage{amsmath}
\usepackage{lipsum}
\begin{document}
\lipsum[1]
\begin{multline}
a_1 + b_1 + c_1 + d_1 + e_1 + f_1\\
\shoveright{g_1 + h_1 + i_1 + j_1 + k_1 + l_1}\\
\shoveleft{a_2 + b_2 + c_2 + d_2 + e_2 + f_2}\\
g_2 + h_2 + i_2 + j_2 + k_2 + l_2
\end{multline}
\lipsum[2]
\end{document}
Addendum
As pointed out by @barbara beeton, the position of the equation number is ambiguous. This can be solved by using the subsidiary environment multlined provided by mathtools inside an equation (first proposed by @egreg). This approach also benefits from the improved spacing of the equation environment.
\usepackage{mathtools}
\begin{equation}
\begin{multlined}[.7\textwidth]
a_1 + b_1 + c_1 + d_1 + e_1 + f_1\\
\shoveright{g_1 + h_1 + i_1 + j_1 + k_1 + l_1}\\
\shoveleft{a_2 + b_2 + c_2 + d_2 + e_2 + f_2}\\
g_2 + h_2 + i_2 + j_2 + k_2 + l_2
\end{multlined}
\end{equation}
You should add the fleqn option to your document class. Regardless, the following is the correct way of using eqnarray:
\documentclass[fleqn]{article}
\begin{document}
\begin{eqnarray}
\Psi_{1}(x,\lambda) & = & U(x,\lambda)e_{1}\label{eqn07}
\end{eqnarray}
\end{document}
You'll notice that the equation is left-aligned, although not flush with the left margin. To achieve this, add \setlength{\mathindent}{0pt} to the document preamble as well.
Note that you don't need eqnarray for a single equation. For this, the equation environment is sufficient. However, since the spacing of eqnarray is inferior to the regular math spacing, it might be better for consistency.
Best Answer
The trick is to underline the parts to the left and the right of the
&separately. The\mathstruts are used to vertically align the two halves and add extra space before the=and below the denominator. For large structures one can use\vphantomto equalize the depths.