# Aligning long set of equations

I'm trying to make a big series of equation equalities in LaTeX, however, my equation just keeps going on out of the page width. Here is what I have:

$$TCU_{1,2}(y_1,y_2)=\frac{25}{4y_1}+\frac{125}{120-y_1} =\frac{25(120-y_1)}{(4y_1)(120-y_1)}+\frac{125(4y_1)}{(120-y_1)(4y_1)} \\ =\frac{25(120-y_1)+125(4y_1)}{(120-y_1)(4y_1)}=\frac{3000+475y_1}{(120-y_1)(4y_1)}$$


I need it to align beneath each other, how do I do this? I only use the amsmath package. and an article documentclass.

• Welcome to TeX.SX! You can have a look at our starter guide to familiarize yourself further with our format. – karlkoeller Jan 10 '15 at 19:56

Use split inside equation*

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{equation*}
\begin{split}
TCU_{1,2}(y_1,y_2)&=\frac{25}{4y_1}+\frac{125}{120-y_1} \\
&=\frac{25(120-y_1)}{(4y_1)(120-y_1)}+\frac{125(4y_1)}{(120-y_1)(4y_1)} \\
&=\frac{25(120-y_1)+125(4y_1)}{(120-y_1)(4y_1)}\\
&=\frac{3000+475y_1}{(120-y_1)(4y_1)}
\end{split}
\end{equation*}
\end{document}


If you want to number the equation, use the equation environment instead of equation*.

Also, don-t use $$..$$ in LaTeX. See Why is $...$ preferable to $$...$$? for reference.

Here I use a left-aligned stack. The interline gap is settable with \setstackgap{S}{gap-size}. The default Shortstack gap is 3pt, which seems to small for my taste in this situation.

\documentclass{article}
\usepackage{amsmath}
\usepackage[usestackEOL]{stackengine}
\stackMath
\setstackgap{S}{8pt}% SETS GAP BETWEEN STACK LINES
\begin{document}
\begin{equation*}
TCU_{1,2}(y_1,y_2)\Shortunderstack[l]{
{}=\dfrac{25}{4y_1}+\dfrac{125}{120-y_1} \\
{}=\dfrac{25(120-y_1)}{(4y_1)(120-y_1)}+\dfrac{125(4y_1)}{(120-y_1)(4y_1)} \\
{}=\dfrac{25(120-y_1)+125(4y_1)}{(120-y_1)(4y_1)}\\
{}=\dfrac{3000+475y_1}{(120-y_1)(4y_1)}
}
\end{equation*}
\end{document}


The identical result could be obtained with a TABstack:

\documentclass{article}
\usepackage{amsmath}
\usepackage{tabstackengine}
\stackMath
\setstackgap{S}{8pt}% SETS GAP BETWEEN STACK LINES
\begin{document}
\begin{equation*}
\alignShortunderstack{%
TCU_{1,2}(y_1,y_2)
=&\dfrac{25}{4y_1}+\dfrac{125}{120-y_1} \\
=&\dfrac{25(120-y_1)}{(4y_1)(120-y_1)}+\dfrac{125(4y_1)}{(120-y_1)(4y_1)} \\
=&\dfrac{25(120-y_1)+125(4y_1)}{(120-y_1)(4y_1)}\\
=&\dfrac{3000+475y_1}{(120-y_1)(4y_1)}
}
\end{equation*}
\end{document}

• I think I said it before, but I will say it again: the interface for that package is awful (just my opinion, don't worry), I think you should think about a better interface (proably with key-value optional arguments). It would gain usability and users. – Manuel Jan 11 '15 at 2:37
• @Manuel I appreciate your input. – Steven B. Segletes Jan 11 '15 at 2:40
• Rereading, it may seem like “bad words”, I meant no “aggression”; while I really think your packages are useful, they lack of an acceptable interface. – Manuel Jan 11 '15 at 2:47
• @Manuel I take it in the spirit in which it was intended, namely constructive criticism. Given lots of free time, I would move upon it, but that commodity has been in relatively short supply of late. – Steven B. Segletes Jan 11 '15 at 2:52