Bài 7:
a) Ta có: \(\left|\dfrac{1}{2}-x\right|\ge0\forall x\)
\(\Leftrightarrow\left|\dfrac{1}{2}-x\right|+10\ge10\forall x\)
Dấu '=' xảy ra khi \(x=\dfrac{1}{2}\)
b) Ta có: \(\left|x+1.5\right|\ge0\forall x\)
\(\Leftrightarrow\left|x+1.5\right|-5.7\ge-5.7\forall x\)
Dấu '=' xảy ra khi x=1,5
Bài 8:
a) Ta có: \(-\left|x+2.1\right|\le0\forall x\)
\(\Leftrightarrow-\left|x+2.1\right|+1.5\le1.5\forall x\)
Dấu '=' xảy ra khi x=-2,1
b) Ta có: \(-\left|2.7-x\right|\le0\forall x\)
\(\Leftrightarrow-\left|2.7-x\right|-5.7\le-5.7\forall x\)
Dấu '=' xảy ra khi x=2,7
Bài 6:
a) Ta có: \(\left|x\right|\ge0\forall x\)
\(\Leftrightarrow\left|x\right|+\dfrac{6}{13}\ge\dfrac{6}{13}\forall x\)
Dấu '=' xảy ra khi x=0
b) Ta có: \(\left|x+2.8\right|\ge0\forall x\)
\(\Leftrightarrow\left|x+2.8\right|-7.9\ge-7.9\forall x\)
Dấu '=' xảy ra khi x=-2,8
