当方程的长度不同时，如何排列方程式？

Question

我有一组长度差异较大的方程式。前两个方程式很短，后两个方程式很长。

问题。如何排列方程式以提高可读性？

\documentclass[12pt]{article}
\usepackage{amsmath} 

\begin{document}
\begin{eqnarray}\label{EQ4}
\alpha_{0} &=&1-\frac{t}{h},  \\ \nonumber
%
\alpha _{1} &=&\frac{t}{h},  \\ \nonumber
%
\alpha _{2} &=&\frac{1}{2520} \frac{756h^{3} +135h}{h^{3}}
-\frac{1}{7560} \frac{(1869h^{4} +1950h^{2} +70)t}{h^{3} }
+\frac{1}{270} \frac{\left(54h^{3} +15h\right)\left(\frac{5}{2}
t^{2} -\frac{3}{2} \right)}{h^{3} } \\ \nonumber &-&
\frac{1}{6930} \frac{\left(715h^{2} +42\right)\left(\frac{7}{2}
t^{3} -\frac{5}{2} x+\frac{5}{2} x_{n} \right)}{h^{3} }
-\frac{1}{63} \frac{\frac{63}{8} t^{4} -\frac{35}{4} t^{2}
+\frac{15}{8} }{h^{2} } -\frac{2}{185} \frac{\frac{99}{8} t^{5}
-\frac{63}{4} t^{3} +\frac{35}{8} x-\frac{35}{8} x_{n} }{h^{3} },
\\ \nonumber
%
\alpha _{3} &=&-\frac{1}{4h^{} } -\frac{1}{1260}
\frac{\left(651h^{4} -900h^{2} -70\right)t}{h^{3} } -\frac{7}{27}
\frac{\frac{5}{2} t^{2} -\frac{3}{2} }{h^{2} } +\frac{2}{1155}
\frac{\left(165h^{2} +21\right)\left(\frac{7}{2} t^{3}
-\frac{5}{2} t\right)}{h^{3} } \\ \nonumber &-& \frac{2}{27}
\frac{\frac{63}{8} t^{4} -\frac{35}{4} t^{2} +\frac{15}{8} }{h^{2}
} +\frac{4}{495} \frac{\frac{99}{8} t^{5} -\frac{63}{4} t^{3}
+\frac{35}{8} t}{h^{3} },  \\ \nonumber

\end{eqnarray}    
\end{document}

Answer 1

这是一种可能性，使用align和\medsize来自的命令nccmath：

\documentclass[12pt]{article}
\usepackage[a4paper, showframe]{geometry}
\usepackage{mathtools, nccmath}

\begin{document}

\begin{align}\label{EQ4}
\alpha_{0} &= 1-\frac{t}{h}, \\ \nonumber
%
\alpha _{1} &= \frac{t}{h}, \\ \nonumber
%
\alpha _{2} &=\medmath{\begin{aligned}[t] \frac{1}{2520} \frac{756h^{3} +135h}{h^{3}}
-\frac{1}{7560} \frac{(1869h^{4} +1950h^{2} +70)t}{h^{3} }
+\frac{1}{270} \frac{\left(54h^{3} +15h\right)\biggl({5}{2}
t^{2} -\cfrac{3}{2} \biggr)}{h^{3} } \\-
\frac{1}{6930} \frac{\left(715h^{2} +42\right)\left(\dfrac{7}{2}
t^{3} -\dfrac{5}{2} x+\dfrac{5}{2} x_{n} \right)}{h^{3} } %\\ \nonumber
-\frac{1}{63} \frac{\dfrac{63}{8} t^{4} -\dfrac{35}{4} t^{2}
+\dfrac{15}{8} }{h^{2}}\\ -\frac{2}{185} \frac{\dfrac{99}{8} t^{5}
-\dfrac{63}{4} t^{3} +\dfrac{35}{8} x-\dfrac{35}{8} x_{n} }{h^{3}},
\end{aligned}}\nonumber\\[1.5ex]
%
\alpha _{3} &=\medmath{\begin{aligned}[t] -\frac{1}{4h^{} } -\frac{1}{1260}
\frac{\left(651h^{4} -900h^{2} -70\right)t}{h^{3} } -\frac{7}{27}
\frac{\dfrac{5}{2} t^{2} -\dfrac{3}{2} }{h^{2} } +\frac{2}{1155}
\frac{\left(165h^{2} +21\right)\left(\dfrac{7}{2} t^{3}
-\dfrac{5}{2} t\right)}{h^{3}} \\- \frac{2}{27}
\frac{\dfrac{63}{8} t^{4} -\dfrac{35}{4} t^{2} +\dfrac{15}{8}}{h^{2}
} +\frac{4}{495} \frac{\dfrac{99}{8} t^{5} -\dfrac{63}{4} t^{3}
+\dfrac{35}{8} t}{h^{3}} ,
\end{aligned}} \nonumber
\end{align}

\end{document} 

Answer 2

或者，您可以使用multlined数学环境，\mfrac而不是\dfrac：

\documentclass[12pt]{article}
\usepackage[a4paper]{geometry}
\usepackage{mathtools, nccmath}

%---------------- show page layout. don't use in a real document!
\usepackage{showframe}
\renewcommand\ShowFrameLinethickness{0.15pt}
\renewcommand*\ShowFrameColor{\color{red}}
%---------------------------------------------------------------%

\begin{document}

\begin{align}\label{EQ4}
\alpha_{0}  & = 1-\frac{t}{h},          \\
%
\alpha_{1}  & = \frac{t}{h},    \notag  \\
%
\alpha_{2}  & = \medmath{\begin{multlined}[t]
    \frac{1}{2520}\frac{756h^{3} + 135h}{h^{3}}
    -\frac{1}{7560}\frac{(1869h^{4} + 1950h^{2} + 70)t}{h^{3}}  \\
    +\frac{1}{270}\frac{\left(54h^{3} + 15h\right)
    \left({5}{2}t^{2} - \mfrac{3}{2} \right)}{h^{3} }
        - \frac{1}{6930}\frac{\left(715h^{2} + 42\right)
        \left(\mfrac{7}{2}t^{3} - \mfrac{5}{2} x + \mfrac{5}{2} x_{n} \right)}{h^{3} }                                    \\
        -\frac{1}{63} \frac{\mfrac{63}{8} t^{4} - \mfrac{35}{4} t^{2}
        + \mfrac{15}{8} }{h^{2}}
        - \frac{2}{185} \frac{\mfrac{99}{8} t^{5}
        -\mfrac{63}{4} t^{3} +\mfrac{35}{8} x-\mfrac{35}{8} x_{n} }{h^{3}},
        \end{multlined}}        \notag  \\[2ex]
%
\alpha_{3}  & = \medmath{\begin{multlined}[t]
    -\frac{1}{4h^{} } -\frac{1}{1260}\frac{\left(651h^{4} - 900h^{2} -70\right)t}{h^{3} } - \frac{7}{27}\frac{\mfrac{5}{2} t^{2}  -\mfrac{3}{2} }{h^{2} } \\
    + \frac{2}{1155}\frac{\left(165h^{2} + 21\right)\left(\mfrac{7}{2} t^{3}
    -\mfrac{5}{2} t\right)}{h^{3}}
    - \frac{2}{27}\frac{\mfrac{63}{8} t^{4} - \mfrac{35}{4} t^{2} + \mfrac{15}{8}}{h^{2}} + \frac{4}{495} \frac{\mfrac{99}{8} t^{5} -\mfrac{63}{4} t^{3} +\mfrac{35}{8} t}{h^{3}} ,
                        \end{multlined}} \notag
\end{align}
\end{document}