3.26.2 Greatest hits from previous weeks

Greatest hits from previous weeks:

3.26.2.1 inputenc Error: Unicode char \u8: not set up for use with LaTeX

https://tex.stackexchange.com/questions/83440/inputenc-error-unicode-char-u8-not-set-up-for-use-with-latex

This is with ref to my previous question Package clash in multilingual report. 
\documentclass[11pt,table,a4paper]{article} 
\usepackage{lmodern} 
\usepackage[utf8]{inputenc} 
\usepackage[T1]{fontenc} 
...
 

- asked by Manish (80 votes), answered by egreg (63 votes)

3.26.2.2 How to write cases with LaTeX?

https://tex.stackexchange.com/questions/240868/how-to-write-cases-with-latex

The code i used to write 
is this one 
$$ 
X(m,n)= 
\begin{cases} 
x(n),\\ 
x(n-1)\\ 
x(n-1) 
\end{cases} 
$$ 
But I don't know how to write this one 
I appreciate any help. 
Edited: I'm sorry to add  ...
 

- asked by marya (55 votes), answered by Ignasi (39 votes)