Vì |x+300|>=0, |500+x|>=0
=>|500+x|+|x+300|>=0
Nên MIN A =0
Ta có: A= \(|x-500|+|x-300|\)
=\(|x-500|+|300-x|\)
Áp dụng: \(|x|+|y|\ge|x+y|\)
\(\Rightarrow A\ge|x-500+300-x|\)
\(\Rightarrow A\ge|-200|\Leftrightarrow A\ge200\)
Để A đạt GTNN \(\Rightarrow|x-500|+|300-x|\)
\(\Leftrightarrow\)\(x-500\ge0\) \(\Rightarrow\)\(x\ge500\)
\(\Leftrightarrow\) \(300-x\ge0\) \(\Rightarrow\)\(x\le300\)
\(\Leftrightarrow\)\(x-500< 0\) \(\Rightarrow\)\(x>500\)
\(\Leftrightarrow\)\(300-x>0\) \(\Rightarrow\)\(x< 300\)
\(\Rightarrow\)\(300\le x\le500\)
Vậy A có GTNN = 200 khi và chỉ khi \(300\le x\le500\)
k mk nhé! Thank you very much!