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heyy:)

I try to write an equation using \alpha , \beta, \delat and \gamma inside the equation of LaTex. And I use split such that i have multiple lines inside the equation without numbering all the lines individually

\begin{equation}
\begin{split}
    f'(x',y') &= [a\alpha^2 + b\alpha\gamma]\: x'^2 \\
    &+ [b(\alha\delta + \beta\gamma)+ 2(a\alpha\beta - c\gamma\delta]\:x'y' \\
    &+ [a\beta^2 + b\beta\delta + c\delta^2]\:y'^2
\end{split}
\end{equation}

The output should be like this:

f′(x′,y′) = [aα2 + bαγ] x′2
          + [b(δ + βγ) + 2(aαβ − cγδ] x′y′                      (1)
          + [aβ2 + bβδ + cδ2] y′2

But i get the error undefined control sequence. Does someone know how I need to write this equation such that it works? These are my packages:

\documentclass[12pt]{article}

\usepackage[margin=1in]{geometry} 
\usepackage{amsmath,amsthm,amssymb}

\usepackage[dvipsnames]{xcolor}

\usepackage{cmbright}
\usepackage[OT1]{fontenc}
4
  • 3
    well really look at the error message. It tells you which command is undefined. And then correct alha to alpha. Dec 5, 2023 at 10:30
  • If you don't see which control sequence is undefined in the error message then something is wrong. Maybe your user interface which you are running TeX doesn't print it. Then I recommend: replace such a user interface by better one.
    – wipet
    Dec 5, 2023 at 10:44
  • 1
    some editors hide the error message (texstudio is spectacularly bad with undefined command errors) always check the log file. Also only use split if you need its complexity, I would use aligned here and in almost all cases. Dec 5, 2023 at 10:46
  • Thanks a lot:) Im not very used to read error messages in LaTex therefore I just missed this.
    – Pluschein
    Dec 5, 2023 at 11:21

2 Answers 2

1

You have misspelt \alpha

\begin{equation}
\begin{split}
    f'(x',y') &= [a\alpha^2 + b\alpha\gamma]\: x'^2 \\
    &+ [b(\alpha\delta + \beta\gamma)+ 2(a\alpha\beta - c\gamma\delta]\:x'y' \\
    &+ [a\beta^2 + b\beta\delta + c\delta^2]\:y'^2
\end{split}
\end{equation}

Hope that helps

1
  • Thanks a lot:) I just didn't see that and tried some crazy stuff instead :')
    – Pluschein
    Dec 5, 2023 at 11:22
2

You did not show the error message.

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{equation}
\begin{split}
    f'(x',y') &= [a\alpha^2 + b\alpha\gamma]\: x'^2 \\
    &+ [b(\alha\delta + \beta\gamma)+ 2(a\alpha\beta - c\gamma\delta]\:x'y' \\
    &+ [a\beta^2 + b\beta\delta + c\delta^2]\:y'^2
\end{split}
\end{equation}
\end{document}

Produces the error

! Undefined control sequence.
<argument> ...lpha \gamma ]\: x'^2 \\ &+ [b(\alha 
                                                  \delta + \beta \gamma )+ 2...
l.9 \end{split}
               
? 

This higlights the undefined command \alha by the linebreak.

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  • 1
    Just a hint for the OP. this looks beter if you in the first line replace &= by = {} &, then the starting + on the other lines are quitable indented and not listed under the = (which IMO they should not)
    – daleif
    Dec 5, 2023 at 10:58

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