2

What wrong with that?

\begin{eqnarray}
    {v}_{sa}=m_{a}\frac{V_{d}}{2}cos(\omega_{1}t)\\
    {v}_{sb}=m_{a}\frac{V_{d}}{2}cos(\omega_{1}t -\frac{2\pi}{3})\\
    {v}_{sn}=m_{a}\frac{V_{d}}{2}cos(\omega_{1}t +\frac{2\pi}{3})\\
    \label{current_rel1}
\end{eqnarray}

I want to get vsa ... vsb ... vsn:

 V_sa=...
 V_sb=...
 V_sn=...

Someone can help solving that?

5
  • Welcome to TeX.SX! Please help us help you and add a minimal working example (MWE) that illustrates your problem. Reproducing the problem and finding out what the issue is will be much easier when we see compilable code, starting with \documentclass{...} and ending with \end{document}.
    – Troy
    Dec 28, 2016 at 15:02
  • Welcome to TeX SX! You have specified no alignment points. Anyway, eqnarray is deprecated and gives bad spacing. Replace it with the align environment, from amsmath.
    – Bernard
    Dec 28, 2016 at 15:03
  • 1
    Generally the advice is to use the align environment from amsmath rather than eqnarray (eqnarray vs align), in order to specify alignment points you need to place & at the alignment points, one & when using align and two when using eqnarray. See this answer for an example with align.
    – Dai Bowen
    Dec 28, 2016 at 15:05
  • 2
    You should definitely replace cos with \cos. Also, I know of no advantage to having {v}_{sa} instead of just v_{sa}
    – Au101
    Dec 28, 2016 at 15:08
  • great,That works.
    – user121793
    Dec 28, 2016 at 15:11

2 Answers 2

4

Maybe one of these is what you want?

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{equation}
  \begin{aligned}
    v_{sa} & =m_{a}\frac{V_{d}}{2}\cos(\omega_{1}t) \\
    v_{sb} & =m_{a}\frac{V_{d}}{2}\cos\Bigl(\omega_{1}t -\frac{2π}{3}\Bigr) \\
    v_{sn} & =m_{a}\frac{V_{d}}{2}\cos\Bigl(\omega_{1}t +\frac{2π}{3}\Bigr)
    \label{current_rel1}
  \end{aligned}
\end{equation}

  \begin{align}
    v_{sa} & =m_{a}\frac{V_{d}}{2}\cos(\omega_{1}t) \label{current_rel2} \\
    v_{sb} & =m_{a}\frac{V_{d}}{2}\cos\Bigl(\omega_{1}t -\frac{2π}{3}\Bigr) \label{current_rel3} \\
    v_{sn} & =m_{a}\frac{V_{d}}{2}\cos\Bigl(\omega_{1}t +\frac{2π}{3}\Bigr)
    \label{current_rel4}
  \end{align}

\begin{subequations}
  \begin{align}
    v_{sa} & =m_{a}\frac{V_{d}}{2}\cos(\omega_{1}t) \label{current_rel1a} \\
    v_{sb} & =m_{a}\frac{V_{d}}{2}\cos\Bigl(\omega_{1}t -\frac{2π}{3}\Bigr) \label{current_rel1b} \\
    v_{sn} & =m_{a}\frac{V_{d}}{2}\cos\Bigl(\omega_{1}t +\frac{2π}{3}\Bigr)
    \label{current_rel1c}
  \end{align}
\end{subequations}

\end{document}

enter image description here

2
  • 1
    The original code has all three equations numbered. Can you add the alternative code for that?
    – egreg
    Dec 28, 2016 at 15:56
  • @egreg: I'll add it, but there was only one label, from which I inferred it was meant as a whole.
    – Bernard
    Dec 28, 2016 at 18:50
2

Some suggestions:

  • Don't use the eqnarray environment: It's badly deprecated. Avoid eqnarray! Instead of eqnarray, use the align environment that's provided by the amsmath package. See the posting eqnarray vs align for more information on this subject.

  • Don't forget to provide alignment points. (Your current code needs &=& instead of just =.) For the align environment, place & before = in order to achieve alignment on the = symbols.

  • Write \cos instead of cos to get the term to behave like a math operator.

  • Either create larger parentheses around the arguments of \cos or use smaller fractions.

enter image description here

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{align}
    v_{sa}&=\tfrac{1}{2}m_{a}V_d\cos(\omega_{1}t)\\
    v_{sb}&=\tfrac{1}{2}m_{a}V_d\cos(\omega_{1}t -\tfrac{2}{3}\pi)\\
    v_{sn}&=\tfrac{1}{2}m_{a}V_d\cos(\omega_{1}t +\tfrac{2}{3}\pi) \label{current_rel1}
\end{align}
\end{document}

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