\(B=\frac{x^2+2x+2019}{x^2}=\frac{x^2+x+x+1+2018}{x^2}=\frac{x\left(x+1\right)+\left(x+1\right)+2018}{x^2}=\frac{\left(x+1\right)^2+2018}{x^2}\)
Vì \(\left(x+1\right)^2\ge0\Rightarrow\left(x+1\right)^2+2018\ge2018\Rightarrow B=\frac{\left(x+1\right)^2+2018}{x^2}\ge\frac{2018}{x^2}\)
Dấu "=" xảy ra khi x=-1
Vậy Bmin = 2018/x^2 khi x=-1
P/s: ko chắc lắm :v