Question

[nguyen thi ngoc tram]

tim GTNN cua bieu thuc

A = / x + 3 / + / x - 9 /

Answer 1

[Blue Moon]

\(A=|x+3|+|x-9|=|x+3|+|9-x|\ge|x+3+9-x|=12.\)

Dấu "=" xảy ra \(\Leftrightarrow\left(x+3\right)\left(9-x\right)\ge0\)

\(\Leftrightarrow-3\le x\le9\)

Vậy: Amin=12\(\Leftrightarrow-3\le x\le9\)