Question

Tìm GTLN
3 - 2 (3x+1)²

Answer 1

Ta có: \(A=3-2\left(3x+1\right)^2\le3\)

Dấu " = " khi \(2\left(3x+1\right)^2=0\Leftrightarrow x=\dfrac{-1}{3}\)

Vậy \(MIN_A=3\) khi \(x=\dfrac{-1}{3}\)

Answer 2

Ta có: \(2\left(3x+1\right)^2\ge0\forall x\)

\(\Rightarrow-2\left(3x+1\right)^2\le0\forall x\)

\(\Rightarrow3-2\left(3x+1\right)^2\le3\forall x\)

Dấu "=" xảy ra \(\Leftrightarrow3x+1=0\Rightarrow x=\dfrac{-1}{3}\)

Vậy MAX \(3-2\left(3x+1\right)^2=3\Leftrightarrow x=\dfrac{-1}{3}\)