# how to write this this long equation?

  \begin{align}\nonumber
(A_{1}^{5}+A_{8}^2)\tt_{m}^{2}\k^{2}P_{m}^{5}-\left(2(A_{1}^{2}+A_{2}^2)
(\Delta_{a}-\omega_{m}\chi^{2}C)\omega_{m}\chi^{2}-2J^{2}\omega_{m}\chi^{2}
(\kappa_{a}A_{2}-\Delta_{d}A_{1})\right)P_{m}^4\\
\nonumber
&&+((\kt_{a}A_{1}+J^{2}\om_{d})^2+
(\kappa_{a}A_{1}+J^{2}\Delta_{d})^2+
(\Delta_{a}-\omega_{m}\chi^{2}C)^2(A_{1}^{5}+A_{7}^2)+2J^{2}(\Delta_{a}-
\omega_{m}\chi^{5}C)(\Delta_{d}A_{1}-\kappa_{a}A_{9}))P_{m}^2\\
\nonumber
&=&\left|\x_{0}\right|^{2}(m_{1}^{2}+n_{2}^5)+2\kp_{0}A_{2}gJ\S
Cos[m]N+J^{2}gk^{2}S^{2}N^{2}
\tag{M1}
\end{align}

• please extend your code fragment to small, self contained document, which have define \k . Do you really need \S symbol in equation or you give it some new meaning? What is Cos?Just three variables? Your question is unclear. – Zarko Aug 30 '19 at 7:17
• What is your document class? Which font size? Do you use the standard layout? – Bernard Aug 30 '19 at 8:05

Since you not provide MWE (Minimal Working Example, a small complete document which we can test as it is), we haven't any information about your document layout, used packages relevant to your equation and about eventual defined new commands or math operators.

Also is not clear, why you require that part of equation use \tt fonts (btw, correct is \ttfamily) and what means in your equation symbol \S (section sign) in your equation (usually used in legal documents). Further, which coding you use (where is define \k symbol)

With use of standard article document class, fonts newtxmath, packages mathtools and nccmath, and breaking your equation into four lines I managed to obtain the following result: (red lines indicate text border)

\documentclass{article}
\usepackage{newtxtext,newtxmath}
\usepackage{mathtools,nccmath}
\DeclarePairedDelimiter\abs{\lvert}{\rvert}

\begin{document}
\begin{equation}\tag{M1}
\medmath{
\begin{aligned}
\bigl(A_{1}^{5}
+ & A_{8}^2\bigr)_{m}^{2}k^{2}P_{m}^{5} -
\Bigl(2\bigl(A_{1}^{2}+A_{2}^2\bigr)
\bigl(\Delta_{a} - \omega_{m}\chi^{2}C\bigr)
\omega_{m}\chi^{2}-2J^{2}\omega_{m}\chi^{2}
\bigl(\kappa_{a}A_{2}-\Delta_{d}A_{1}\bigr)\Bigr)P_{m}^4    \\
+ & \Bigl(\bigl(kt_{a}A_{1}+J^{2}om_{d}\bigr)^2+
\bigl(\kappa_{a}A_{1}+J^{2}\Delta_{d}\bigr)^2 +
\bigr(\Delta_{a}-\omega_{m}\chi^{2}C\bigl)^2
\bigl(A_{1}^{5}+A_{7}^2\bigr)                               \\
+ & 2J^{2}\bigl(\Delta_{a} - \omega_{m}\chi^{5}C\bigr)
\bigl(\Delta_{d}A_{1}-\kappa_{a}A_{9}\bigr)\Bigr)P_{m}^2    \\
= & \abs{x_{0}}^{2}\bigl(m_{1}^{2}+n_{2}^5\bigr) +
2kp_{0}A_{2}gJ\S
Cos[m]N+J^{2}gk^{2}S^{2}N^{2}
\end{aligned}
}
\end{equation}
\end{document}


Your MWE having some errors, e.g., \k, \kt, etc. I just removed just \ for compiling purpose, and the modified codes are given below:

\documentclass{book}
\usepackage{mathtools}

\begin{document}

\begin{align}\nonumber
(A_{1}^{5}+A_{8}^2)\tt_{m}^{2}k^{2}P_{m}^{5}&-\left(2(A_{1}^{2}+A_{2}^2)
(\Delta_{a}-\omega_{m}\chi^{2}C)\omega_{m}\chi^{2}-2J^{2}\omega_{m}\chi^{2}
(\kappa_{a}A_{2}-\Delta_{d}A_{1})\right)P_{m}^4\\
+((kt_{a}A_{1}+J^{2}om_{d})^2+
(\kappa_{a}A_{1}+J^{2}\Delta_{d})^2+
(\Delta_{a}-\omega_{m}\chi^{2}C)^2(A_{1}^{5}+A_{7}^2)\\
\omega_{m}\chi^{5}C)(\Delta_{d}A_{1}-\kappa_{a}A_{9}))P_{m}^2\\
&\nonumber
=\left|x_{0}\right|^{2}(m_{1}^{2}+n_{2}^5)+2kp_{0}A_{2}gJ\S
Cos[m]N+J^{2}gk^{2}S^{2}N^{2}
\tag{M1}
\end{align}
\end{document}


Note that, I've break the equations per standard format...

• You could use align* (starred form) so that adding \nonumber is not needed – user94293 Aug 30 '19 at 7:18
• @user94293 But the OP is giving the equation number as M1 as in \tag command in the last set of equation... – MadyYuvi Aug 30 '19 at 7:19
• In this case the simplest is to use an equation environment, and inside, insert \begin{aligned}[b]. – Bernard Aug 30 '19 at 7:54
• @Bernard Agreed your statement, really that's the nice way, shall I change my answer? – MadyYuvi Aug 30 '19 at 8:22
• No problem if you want to, but there's something else: if the margins are the standard margins, there's an overfull \hbox message. – Bernard Aug 30 '19 at 8:24