Áp dụng BĐT \(\left|a\right|+\left|b\right|\ge\left|a+b\right|\) ta có:
\(H=\left|x-3\right|+\left|4+x\right|\)\(=\left|x-3\right|+\left|-\left(4+x\right)\right|\)
\(=\left|x-3\right|+\left|-4-x\right|\ge\left|x-3+\left(-4\right)-x\right|=7\)
Dấu "=" xảy ra khi \(-4\le x\le3\)