Question

Tìm GTLN:

a,A=6x−x2a,

b,B=6−8x−x2

Answer 1

\(B=-x^2-8x+6\)

\(=-\left(x^2+8x-6\right)\)

\(=-\left(x^2+8x+16-22\right)\)

\(=-\left(x+4\right)^2+22\le22\)

Dấu '=' xảy ra khi x=-4

Answer 2

`a,A=6x-x^2`

`A=−(x^2−6x)`

`A=−(x^2−6x+9)+9`

`A=−(x−3)^2+9`

Vì `(x−3)^2≥0∀x`

`⇔ (x−3)^2≥0`

`⇒ −(x−3)^2≤0`

`⇒ −(x−3)^2+9≤9`

`A≤9`

Dấu `"="` xảy ra khi: `x−3=0→x=3`

Vậy `Max A` `=9` khi `x=3`