I am making a math formulary collection but the file is getting too big and too long!

So i was wondering if it is possible to make a .tex for for multiplication and one .tex file for division. And then make a third .tex file where i am importing the other two files and still be able to make TOC?
and lets say each .tex files also have multiple sections and sub(sub)sections

In order to selectively include parts of your document and still get page numbers and table of contents right, you can use include and includeonly. Your main file should look like this:

documentclass{whatever}

% put preamble here



% includeonly{mult}

% includeonly{div}

% includeonly{mult,div}

begin{document}

tableofcontents

include{mult}

include{div}

end{document}

The files mult.tex and div.tex should then only contain the corresponding text and formulas, but no preamble (no documentclass, no begin{document}, etc.).

Note that include always starts a new page. This is necessary in order to get consistent layout and page numbers. On the other hand, input does not insert a new page, but then you do not get the right table of contents, and page numbers change when you comment out one of the files.

Applying "divide and conquer" approach to your project -- by splitting your project into several smaller input files -- is a good practice.

In addition to this, it will be better if you can compile each smaller input file so you can see the result on which you focus. Compiling each smaller input file, of course, takes shorter time compared to compiling the project as a whole.

The following imitates your case. Consider you have 2 smaller input files called dif.tex and int.tex. Both are compilable as follows.

dif.tex

documentclass{article}

usepackage{amsmath}



begin{document}

section{Definition}

[

lim_{hto 0}frac{f(x+h)-f(x)}{h} = f'(x)

]



section{Partial differentiation}

[

textrm{d}(AB) = B,textrm{d}A +A,textrm{d}B

]

end{document}

int.tex

documentclass{article}

usepackage{amsmath}



begin{document}

section{Definite integral}

[

int_a^b f(x), textrm{d}x = F(b) - F(a)

]



section{Partial integral}

[

int A, textrm{d}B = AB -int B , textrm{d}A

]

end{document}

Now you can import both smaller files from your main input file (called main.tex) as follows. Note that we need to load docmute in the main.tex. The purpose of this package is to make input only import contents between begin{document} and end{document}.

main.tex

documentclass{article}

usepackage{docmute}

usepackage{amsmath}





begin{document}



input{dif}

input{int}



end{document}

Update based on the additional comments

If your project is structured as follows,

.../main/main.tex

.../main/dif/dif.tex

.../main/int/int.tex

The main.tex has to be slightly modified as follows,

documentclass{article}

usepackage{docmute}

usepackage{amsmath}





begin{document}



input{dif/dif}

input{int/int}



end{document}

You could organize your material in three separate files:

• File mult.tex: Just the body of the multiplication-related material, no preamble, no begin{document}, and no end{document}.




• File div.tex: Just the body of the division-related material, no preamble, no begin{document}, and no end{document}.



• 
  

  File driver.tex, organized as follows:

  
  
  

  documentclass[<options, if any>]{article} % or `report`, or `book`, etc
  
  ... % preamble material, such as page size, etc
  
  begin{document}
  
  tableofcontents
  
  input mult
  
  clearpage
  
  input div
  
  end{document}
  
  

  
  

If you want to compile just the mult material, or just the div material, comment out one of the other input statements, and be sure to recompile twice in order to propagate all changes (including the table of contents).