deletions | additions       diff --git a/untitled.tex b/untitled.tex  index 51e0eb4..d39d1b4 100644  --- a/untitled.tex  +++ b/untitled.tex 
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\selectlanguage{english}$$  \{x(t+1)=x(t)+a*t+2.1+E_{t}\\  \{z(t)=x(t)+N_{k}  $$ \begin{cases}  x(t+1)=x(t)+a*t+2.1+E_{t}\\  z(t)=x(t)+N_{k}  \end{cases}