Question

Tìm GTNN của B=/x-7/+/x+8/
Giúp e vs mn!

Answer 1

\(B=\left|x-7\right|+\left|x+8\right|\)

\(\Rightarrow B=\left|7-x\right|+\left|x+8\right|\)

\(\Rightarrow B\ge\left|7-x+x+8\right|\)

\(\Rightarrow B\ge\left|15\right|\)

\(\Rightarrow B\ge15\)

Dấu "=" xảy ra \(\Leftrightarrow\left(x-7\right)\left(x+8\right)\ge0\)

Vậy \(B_{min}=15\Leftrightarrow\left(x-7\right)\left(x+8\right)\ge0\)