\(\left|2x-7\right|+\left|2x+1\right|=\left|7-2x\right|+\left|2x+1\right|\ge\left|7-2x+2x+1\right|=8\)
mà \(\left|2x-7\right|+\left|2x+1\right|\le8\)
=> dấu "=" phải xra.
Khi đó: \(\left(7-2x\right)\left(2x+1\right)\ge0\)
<=> \(-\frac{1}{2}\le x\le\frac{7}{2}\)
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