Từ giả thiết
<=>M=\(\left|x-4\right|+\left|x-1\right|=\left|x-4\right|+\left|1-x\right|\ge\left|x-4+1-x\right|=3\)
Dấu "=" xảy ra <=> \(\left(x-4\right)\left(1-x\right)\ge0\)
=>\(\left[{}\begin{matrix}1\ge x\ge4\left(ktm\right)\\1\le x\le4\left(tm\right)\end{matrix}\right.\)
Vậy minM=3 <=> \(1\le x\le4\)