a, chon \(Ox\equiv AB,O\equiv A,\) chieu cd tu A->B,moc tgian luc 7h
\(\Rightarrow xA=50t\)
\(\Rightarrow xB=10+40t\)
\(\Rightarrow xA=xB\Leftrightarrow t=1h\Rightarrow B.8h\)
b,\(\Rightarrow Sa=xA=50km\Rightarrow C\)
c,\(\Rightarrow\left|xA-xB\right|=20\Leftrightarrow\left[{}\begin{matrix}10t-10=20\\10t-10=-20\end{matrix}\right.\)\(\Leftrightarrow\left[{}\begin{matrix}t=3h\\t=-1h\left(loai\right)\end{matrix}\right.\)
luc 10h 2 xe cach nhau 20km
vd2: (de mo ko doc dc)
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