# How to create a Fraction equation with '[]' while numerator and denominator may have more than two lines

How to create a Fraction equation with '[]' while numerator and denominator may have more than two lines: The new equation is:

\begin{equation}
q_{2n}^*=\Bigg[
-\frac{(\alpha -1) \alpha  A_0^2 \beta  k^2 \left(\lambda _h-\lambda
_l\right) \left(-c_l \left(\lambda _h-1\right)+c_h \left(\lambda _l-
1\right)+\left(c_n+c_{\text{nature}}-1\right) \left(\lambda _h-\lambda
_l\right)\right)+2 A_0 k \left(\alpha  (\beta -1)+\alpha  \beta  c_h
\left(\lambda _h+1\right)+\alpha  \beta  \lambda _h \left(-2 c_n-2
c_{\text{nature}}-\lambda _h \delta _m+\delta _m+1\right)-(\alpha -1) c_l
\left(\lambda _l+1\right)+\lambda _l \left(-\alpha +2 (\alpha -1) c_n+2
(\alpha -1) c_{\text{nature}}+\alpha  \left(-\delta _m\right)+\delta
_m\right)+\lambda _l+(\alpha -1) \lambda _l^2 \delta _m+1\right)+4
\left(c_n+c_{\text{nature}}-\delta _m\right)}{2 k \left(A_0 k \left(\alpha
(\beta -1)+\alpha  \beta  \lambda _h^2-2 \alpha  \beta  \lambda _h-(\alpha
-1) \left(\lambda _l-2\right) \lambda _l+1\right)+4\right)}
\Bigg]
\end{equation}


It hopes that the above equation could be look like this which created by mathtype: • oh my please don't do this, have mercy on the readers. May 21, 2017 at 8:50

Something like this? Observe the use of square brackets and curly braces in lieu of some round parentheses.

\documentclass{article}
\usepackage{array,amsmath,geometry}
\begin{document}
\begin{equation}
\renewcommand\arraystretch{1.25}
q_{2n}^*=-\frac{ \left[ \begin{array}{@{} >{{}}l @{}}
(\alpha-1)\alpha A_0^2 \beta k^2 (\lambda_h-\lambda_l)
\bigl[-c_l (\lambda_h-1)+c_h (\lambda_l-1) \\
+(c_n+c_{\text{nature}}-1) (\lambda_h-\lambda_l)\bigr]
+2 A_0 k \bigl\{\alpha (\beta -1)+\alpha \beta c_h (\lambda_h+1)\\
+\alpha \beta \lambda_h (-2 c_n-2 c_{\text{nature}}
-\lambda_h \delta_m+\delta_m+1)-(\alpha -1) c_l (\lambda_l+1)\\
+\lambda_l \bigl[-\alpha +2 (\alpha -1) c_n+2 (\alpha -1)
c_{\text{nature}}+\alpha (-\delta_m)+\delta_m\bigr]\\
+\lambda_l+(\alpha -1) \lambda_l^2 \delta_m+1\bigr\}
+4 (c_n+c_{\text{nature}}-\delta_m)
\end{array} \right]
}{2 k \bigl[A_0 k \bigl(\alpha (\beta -1)+\alpha \beta \lambda_h^{2^{\mathstrut}}
-2 \alpha \beta \lambda_h-(\alpha-1) (\lambda_l-2) \lambda_l + 1 \bigr)+4\bigr]}
\end{equation}
\end{document}

• Could you please just explain what does '{@{} >{{}}l @{}}' mean? Thanks so so so much!! May 21, 2017 at 10:07
• @CentrinoGu - The most important particle is l, which indicates that there's a single, left-aligned column in the array environment. The @{} particles instruct LaTeX not to insert any whitespace "padding" to the left and right of the column. Finally, the >{{}} particle instructs LaTeX to prefix each cell with {} (an "empty math atom", in TeX jargon). This is useful because almost all cells of the array start with +. Without the {} prefix, the + symbols would be misinterpreted by TeX as unary instead of as binary operators. (That's an error made by mathtype in 2 instances, BTW.)
– Mico
May 21, 2017 at 12:42