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I tried to split a long equation with numerator and denominator over more lines in different ways (How can I split an equation over two (or more) lines and How to wrap a long equation in Latex), but they do not work (latex gives me error). How can I solve the problem?

The expression (produced by Mathematica) is the following (the splits should occur where there are exponential terms):

y(t) = h(t) = \frac{e^{t
   \left(-\frac{k_1}{2}-\frac{k_2}{2}-\frac{k_{12}}{2}-\frac{k_{21}}{2}-\frac{1}{2
   } \sqrt{\left(k_1+k_2+k_{12}+k_{21}\right){}^2-4 \left(k_1 k_2+k_{21} k_2+k_1
   k_{12}\right)}\right)} k_1 -e^{t
   \left(-\frac{k_1}{2}-\frac{k_2}{2}-\frac{k_{12}}{2}-\frac{k_{21}}{2}+\frac{1}{2
   } \sqrt{\left(k_1+k_2+k_{12}+k_{21}\right){}^2-4 \left(k_1 k_2+k_{21} k_2+k_1
   k_{12}\right)}\right)} k_1-e^{t
   \left(-\frac{k_1}{2}-\frac{k_2}{2}-\frac{k_{12}}{2}-\frac{k_{21}}{2}-\frac{1}{2
   } \sqrt{\left(k_1+k_2+k_{12}+k_{21}\right){}^2-4 \left(k_1 k_2+k_{21} k_2+k_1
   k_{12}\right)}\right)} k_2+e^{t
   \left(-\frac{k_1}{2}-\frac{k_2}{2}-\frac{k_{12}}{2}-\frac{k_{21}}{2}+\frac{1}{2
   } \sqrt{\left(k_1+k_2+k_{12}+k_{21}\right){}^2-4 \left(k_1 k_2+k_{21} k_2+k_1
   k_{12}\right)}\right)} k_2-e^{t
   \left(-\frac{k_1}{2}-\frac{k_2}{2}-\frac{k_{12}}{2}-\frac{k_{21}}{2}-\frac{1}{2
   } \sqrt{\left(k_1+k_2+k_{12}+k_{21}\right){}^2-4 \left(k_1 k_2+k_{21} k_2+k_1
   k_{12}\right)}\right)} k_{12}+e^{t
   \left(-\frac{k_1}{2}-\frac{k_2}{2}-\frac{k_{12}}{2}-\frac{k_{21}}{2}+\frac{1}{2
   } \sqrt{\left(k_1+k_2+k_{12}+k_{21}\right){}^2-4 \left(k_1 k_2+k_{21} k_2+k_1
   k_{12}\right)}\right)} k_{12}+e^{t
   \left(-\frac{k_1}{2}-\frac{k_2}{2}-\frac{k_{12}}{2}-\frac{k_{21}}{2}-\frac{1}{2
   } \sqrt{\left(k_1+k_2+k_{12}+k_{21}\right){}^2-4 \left(k_1 k_2+k_{21} k_2+k_1
   k_{12}\right)}\right)} k_{21}-e^{t
   \left(-\frac{k_1}{2}-\frac{k_2}{2}-\frac{k_{12}}{2}-\frac{k_{21}}{2}+\frac{1}{2
   } \sqrt{\left(k_1+k_2+k_{12}+k_{21}\right){}^2-4 \left(k_1 k_2+k_{21} k_2+k_1
   k_{12}\right)}\right)} k_{21}+e^{t
   \left(-\frac{k_1}{2}-\frac{k_2}{2}-\frac{k_{12}}{2}-\frac{k_{21}}{2}-\frac{1}{2
   } \sqrt{\left(k_1+k_2+k_{12}+k_{21}\right){}^2-4 \left(k_1 k_2+k_{21} k_2+k_1
   k_{12}\right)}\right)} \sqrt{\left(k_1+k_2+k_{12}+k_{21}\right){}^2-4 \left(k_1
   k_2+k_{21} k_2+k_1 k_{12}\right)}+e^{t
   \left(-\frac{k_1}{2}-\frac{k_2}{2}-\frac{k_{12}}{2}-\frac{k_{21}}{2}+\frac{1}{2
   } \sqrt{\left(k_1+k_2+k_{12}+k_{21}\right){}^2-4 \left(k_1 k_2+k_{21} k_2+k_1
   k_{12}\right)}\right)} \sqrt{\left(k_1+k_2+k_{12}+k_{21}\right){}^2-4 \left(k_1
   k_2+k_{21} k_2+k_1 k_{12}\right)}}{2
   \sqrt{\left(k_1+k_2+k_{12}+k_{21}\right){}^2-4 \left(k_1 k_2+k_{21} k_2+k_1
   k_{12}\right)} V_1} 

Thank you for your help.

  • When you want to split equations you shouldn't use \left and \right. But \big (or some other form of the parenthesis resizing. To have the fraction work, you should just split it into multiple fractions of appropriate sizes. – Thorbjørn E. K. Christensen Dec 7 '17 at 15:11
4

I hope I counted well:)

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{align*}
   A&:=\sqrt{(k_1+k_2+k_{12}+k_{21})^2-4(k_1k_2+k_{21}k_2+k_1k_{12})}\\
   B&:=k_1+k_2+k_{12}\\
   C&:=k_1-k_2-k_{12}\\
a(t)&:=\exp\left(-\frac{A+B}{2}t\right)\\
b(t)&:=\exp\left(\frac{A-B}{2}t\right)\\
y(t)&=h(t)=\frac{a(t)(A+C+k_{21})+b(t)(A-C)-k_{21}}{2AV_1} 
\end{align*}
\end{document}

enter image description here

  • 1
    It was elementary mathematics and not LaTeX:) – user91669 Dec 7 '17 at 17:02
  • Hello @tomacs, my goal is to write the whole expression avoiding new definitions. Thank you anyway. – Gennaro Arguzzi Dec 7 '17 at 18:28
  • 1
    @Gennaro Arguzzi -- I'm afraid it is not too good idea. – user91669 Dec 7 '17 at 18:44

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