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%%  Example 02-13-3 
%%  Copyright (C) 2016 Herbert Voss
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\documentclass[]{screxa}
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\usepackage{amsmath}
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\begin{document}
\[
  \begin{split}
    A_{1} & = \left| \int _{0}^{1}(f(x)-g(x))\,\mathrm{d}x\right|
                         +\left| \int _{1}^{2}(g(x)-h(x))\,\mathrm{d}x\right| \\
          & = \left| \int _{0}^{1}(x^{2}-3x)\,\mathrm{d}x\right|
                         +\left| \int _{1}^{2}(x^{2}-5x+6)\,\mathrm{d}x\right| \\
          \intertext{Now the limits of the integrals are used}
          & = \left| \frac{x^{3}}{3}-\frac{3}{2}x^{2}\right| _{0}^{1}
                         +\left| \frac{x^{3}}{3}-\frac{5}{2}x^{2}+6x\right| _{1}^{2}\\
          & = \left| \frac{1}{3}-\frac{3}{2}\right| +\left| \frac{8}{3}-\frac{20}{2}+12-
                         \left( \frac{1}{3}-\frac{5}{2}+6\right) \right| \\
          & = \left| -\frac{7}{6}\right| +\left| \frac{14}{3}-\frac{23}{6}\right| =\frac{7}{6}+
                         \frac{5}{6}=2\, \textrm{FE}
  \end{split}
\]
\end{document}
