Question

tim gtnn b=(8x²-6x+1)/x²

Answer 1

\(B=\dfrac{8x^2-6x+1}{x^2}\)

= \(\dfrac{8x^2}{x^2}-\dfrac{6x}{x^2}+\dfrac{1}{x^2}\)

= \(1-\dfrac{6}{x}+\dfrac{1}{x^2}\)

đặt t=\(\dfrac{1}{x}\) ta có

1-6y+y²

= (y²-6y+9)-8

= (y-3)²-8

do (y-3)² ≥ 0 ∀ x

⇔ (y-3)² -8 ≥ -8

⇔ B ≥ -8

nim B =-8 dấu "=" xảy ra khi

y-3=0 ⇔ y=3 ⇔ \(\dfrac{1}{x}=3\) ⇔ x=\(\dfrac{1}{3}\)

vậy nim B =-8 khi x=\(\dfrac{1}{3}\)