Question

Tìm GTLN

`-x^2+7x-19`

Answer 1

\(=-\left(x^2-7x+19\right)=-\left(x^2-2.\dfrac{7}{2}x+\dfrac{49}{4}+\dfrac{27}{4}\right)\\ =-\left(x-\dfrac{7}{2}\right)^2-\dfrac{27}{4}\le-\dfrac{27}{4}\)

GTLN đạt \(-\dfrac{27}{4}\) khi \(x=\dfrac{7}{2}\)

Answer 2

=-(x^2-7x+19)

=-(x^2-7x+49/4+27/4)

=-(x-7/2)^2-27/4<=-27/4

Dấu = xảy ra khi x=7/2