|x+7,2|-|x-1,2|\(̸\)\(\le\)|x+7,2-x+1,2|=|8,4|=8,4
Dấu " = " xảy ra\(\Leftrightarrow\)(x+7,2)(x-1,2)
\(\Leftrightarrow\)\(\left\{{}\begin{matrix}\left\{{}\begin{matrix}x\le-7,2\\x\ge1,2\end{matrix}\right.\\-7,2\le x\le1,2\left(TM\right)\end{matrix}\right.\left(KTM\right)\)
Vậy |x+7,2|-|x-1,2|=8,4 \(\Leftrightarrow\)-7,2\(\le x\le\)1,2
TH1: x<-7,2
A=-x-7,2-(1,2-x)=-x-7,2-1,2+x=-8,4
TH2: -7,2<=x<1,2
A=x+7,2-(1,2-x)=x+7,2-1,2+x=2x+6
TH3: x>=1,2
A=x+7,2-x+1,2=8,4