2

I want to use this code 

\begin{align}
& \cos(90^\circ-v) = \sin(v)\\ & \sin(90^\circ-v) = \cos(v).
\end{align}

....twice, and have the same numbering of the equations appear to the right of in both ''aligned''. Now, when i put down this code one more time in the same document i get numbering (3) and (4), But I want it to be (1) and (2) as in the first ''align''.

egreg
  • 1,121,712
Henrik
  • 647

1 Answers1

3

Add a \label and use \ref for the repeated display, exploiting the \tag feature that allows arbitrary text for the equation number.

\documentclass{article}
\usepackage{amsmath}

\begin{document}

Here's a display
\begin{align}
\cos(90^\circ-v) &= \sin(v) \label{cos-sin}\\
\sin(90^\circ-v) &= \cos(v).\label{sin-cos}
\end{align}
And again
\begin{align}
\cos(90^\circ-v) &= \sin(v) \tag{\ref{cos-sin}}\\
\sin(90^\circ-v) &= \cos(v).\tag{\ref{sin-cos}}
\end{align}

\end{document}

enter image description here

Don't use degrees when teaching trigonometry, please! ;-)

David Carlisle
  • 757,742
egreg
  • 1,121,712
  • Thanks man, I used degrees so I wouldnt mix it up with radians later. So that i can separate cos(2^\circ) from cos(2) for example – Henrik Dec 17 '13 at 13:31