2 câu trả lời
B=5x- $x^{2}$
=-( $x^{2}$ -5x+ $\frac{25}{4}$ )+ $\frac{25}{4}$
=-(x- $\frac{5}{2}$ )^2+ $\frac{25}{4}$ ≤ $\frac{25}{4}$
∀x
Vậy Max B = $\frac{25}{4}$ khi x- $\frac{5}{2}$ =0
=>x= $\frac{5}{2}$
B=5x- $x^{2}$
=-( $x^{2}$ -5x+ $\frac{25}{4}$ )+ $\frac{25}{4}$
=-(x- $\frac{5}{2}$ )^2+ $\frac{25}{4}$ ≤ $\frac{25}{4}$
∀x
Vậy Max B = $\frac{25}{4}$ khi x- $\frac{5}{2}$ =0
=>x= $\frac{5}{2}$