# How to reference long equations by numbered alphabets [duplicate]

I have 2 long equations when I want to label them as 2a and 2b by using subequation a problem occur that each line of equation n pdf gets number inspite of each equation so thats why i got more numbering than no. of equations

 \begin{subequations} \label{eq2}
\begin{align}
\ddot{x} & = \big( \cos{\phi} \sin{\theta} \cos{\psi} + \sin{\phi} \sin{\psi} \big) \frac{U_1}{m}\\ & \quad - \frac{1}{m} \sum_{i=1}^{4} H_{xi} - K_{fdx} \frac{\dot{x}}{m_s}\\

\ddot{y} & = \big( \cos{\phi} \sin{\theta} \sin{\psi} - \sin{\phi} \sin{\psi} \big) \frac{U_1}{m}\\ & \quad- \frac{1}{m} \sum_{i=1}^{4} H_{yi} - K_{fdy} \frac{\dot{y}}{m_s}\\
\end{align}
\end{subequations}


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• – Sigur Sep 5 '15 at 21:23

Do you mean something like this:

Above equation is obtained by:

    \documentclass{article}
\usepackage{mathtools}

\begin{document}
\begin{subequations}\label{eq2}
\begin{align}
\ddot{x} & = \begin{multlined}[t]
\big(\cos{\phi}\sin{\theta}\cos{\psi} +
\sin{\phi}\sin{\psi}\big)
\frac{U_1}{m}\\
- \frac{1}{m} \sum_{i=1}^{4} H_{xi} - K_{fdx} \frac{\dot{x}}{m_s}
\end{multlined}    \\
\ddot{y} & = \begin{multlined}[t]
\big(\cos{\phi}\sin{\theta}\sin{\psi} -
\sin{\phi}\sin{\psi}\big) \frac{U_1}{m}\\
- \frac{1}{m} \sum_{i=1}^{4} H_{yi} - K_{fdy} \frac{\dot{y}}{m_s}
\end{multlined}
\end{align}
\end{subequations}
\end{document}

• yeah i mean the way u did in 2nd phase actually i cannot manage to write equations in single line as i am doing for a research paper 2 column format so it becomes too wide if i dont use multiple lines environment. Thankx for ur answer – Junaid Anwar Sep 7 '15 at 16:24

I can think of three possibilities.

• Don't split the equations across lines;

• Use \notag on two of the four rows of the align environment;

• Use two split environments within the overall align environment.

The first solution looks like it's the simplest overall. Choosing between solutions 2 and 3 will depend, in part, on whether or not the equation numbers should be centered on each of the pairs of rows.

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\hrule
\begin{subequations} \label{eq2}
\begin{align}
\ddot{x}
&= \big( \cos{\phi} \sin{\theta} \cos{\psi} + \sin{\phi} \sin{\psi} \big) \frac{U_1}{m} - \frac{1}{m} \sum_{i=1}^{4} H_{xi} - K_{fdx} \frac{\dot{x}}{m_s}\\
\ddot{y}
&= \big( \cos{\phi} \sin{\theta} \sin{\psi} - \sin{\phi} \sin{\psi} \big) \frac{U_1}{m} - \frac{1}{m} \sum_{i=1}^{4} H_{yi} - K_{fdy} \frac{\dot{y}}{m_s}
\end{align}
\end{subequations}
\hrule
\begin{subequations} \label{eq4}
\begin{align}
\ddot{x}
&= \big( \cos{\phi} \sin{\theta} \cos{\psi} + \sin{\phi} \sin{\psi} \big) \frac{U_1}{m} \notag\\
&\qquad - \frac{1}{m} \sum_{i=1}^{4} H_{xi} - K_{fdx} \frac{\dot{x}}{m_s}\\
\ddot{y}
&= \big( \cos{\phi} \sin{\theta} \sin{\psi} - \sin{\phi} \sin{\psi} \big) \frac{U_1}{m} \notag\\
&\qquad - \frac{1}{m} \sum_{i=1}^{4} H_{yi} - K_{fdy} \frac{\dot{y}}{m_s}
\end{align}
\end{subequations}
\hrule
\begin{subequations} \label{eq4}
\begin{align}
&\begin{split}\ddot{x}
&= \big( \cos{\phi} \sin{\theta} \cos{\psi} + \sin{\phi} \sin{\psi} \big) \frac{U_1}{m} \\
&\qquad - \frac{1}{m} \sum_{i=1}^{4} H_{xi} - K_{fdx} \frac{\dot{x}}{m_s}
\end{split}\\
&\begin{split}
\ddot{y} &= \big( \cos{\phi} \sin{\theta} \sin{\psi} - \sin{\phi} \sin{\psi} \big) \frac{U_1}{m} \\
&\qquad - \frac{1}{m} \sum_{i=1}^{4} H_{yi} - K_{fdy} \frac{\dot{y}}{m_s}
\end{split}
\end{align}
\end{subequations}
\hrule
\end{document}