Question

Tìm GTNN

A=\(^{x^2}\)+3x-4

Answer 1

\(A=x^2+3x-4\Leftrightarrow x^2+3x+\dfrac{9}{4}-\dfrac{25}{4}\Leftrightarrow\left(x+\dfrac{3}{2}\right)^2-\dfrac{25}{4}\)

ta có \(\left(x+\dfrac{3}{2}\right)^2\ge0\forall x\) \(\Rightarrow\left(x+\dfrac{3}{2}\right)^2-\dfrac{25}{4}\ge\dfrac{-25}{4}\)

\(\Rightarrow\) GTNN của A là \(\dfrac{-25}{4}\) khi \(\left(x+\dfrac{3}{2}\right)^2=0\Leftrightarrow x+\dfrac{3}{2}=0\Leftrightarrow x=\dfrac{-3}{2}\)

vậy GTNN của A là \(\dfrac{-25}{4}\) khi \(x=\dfrac{-3}{2}\)

Answer 2

Sai đề rồi