Sửa đề là tìm GTNN nhé
\(A=2x^2+6x-6\)
\(\Rightarrow A=2\left(x^2+3x-3\right)\)
\(\Rightarrow A=2\left(x^2+3x+\dfrac{9}{4}-\dfrac{21}{4}\right)\)
\(\Rightarrow A=2\left(x^2+3x+\dfrac{9}{4}\right)-2.\dfrac{21}{4}\)
\(\Rightarrow A=2\left(x+\dfrac{3}{2}\right)^2-\dfrac{21}{2}\ge-\dfrac{21}{2}\)
Dấu "=" xảy ra\(\Leftrightarrow x=-\dfrac{3}{2}\)
Vậy \(A_{min}=-\dfrac{21}{2}\Leftrightarrow x=-\dfrac{3}{2}\)
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