Question

Tìm gtln -3x^2+2x

Answer 1

A=-3(x^2 -2x1/3 +1/9)+1/3

  =-3(x-1/3)^2 +1/3

MaxA=1/3 khi x=1/3

Answer 2

Ta có: \(-3x^2+2x=-3\left(x^2-2.\dfrac{4}{3}x+\dfrac{16}{9}\right)+\dfrac{16}{3}=-3\left(x-\dfrac{4}{3}\right)^2+\dfrac{16}{3}\)

Vì \(-3\left(x-\dfrac{4}{3}\right)^2\le0\Leftrightarrow-3\left(x-\dfrac{4}{3}\right)^2+\dfrac{16}{3}\le\dfrac{16}{3}\)

Dấu "=" xảy ra ⇔ \(x=\dfrac{4}{3}\)