\(A=\left|x-1\right|+\left|x-3\right|+\left|x-5\right|+\left|x-7\right|=8\)
\(A=\left|x-1\right|+\left|x-7\right|+\left|x-3\right|+\left|x-5\right|\)
\(A=\left|x-1\right|+\left|7-x\right|+\left|x-3\right|+\left|5-x\right|\)
\(A\ge \left|x-1+7-x\right|+\left|x-3+5-x\right|\)
\(A\ge6+2=8\)
Dấu "=" xảy ra khi: \(3\le x\le5\)