9-10-3.tex

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% 9-10-3.tex
\documentclass{article}
\usepackage{amsmath}
\usepackage{CJK}
\begin{document}
\begin{CJK*}{GBK}{song}
\CJKtilde
\begin{alignat}{2}
    (x^n)' &= nx^{n-1}  &\hspace{20pt} (\sin x)' &= \cos x\\
    (a^x)' &= a^x\ln a  & (\cos x)' &= -\sin x\\
           &            & (\tan x)' &= \frac1{\cos^2x} \label{eq:x}
\end{alignat}

\begin{alignat}{2}
    y &= f(x)+g(x) &\qquad & \text{(由引理\,2)}\\
      &= \sec^2 x  &       & \text{(由\eqref{eq:x}式)}
\end{alignat}
\end{CJK*}
\end{document}