Tìm giới hạn $\Large B=\underset{x\rightarrow 2}{lim}\dfrac{x^4-5x^2+4

Tìm giới hạn $\Large B=\underset{x\rightarrow 2}{lim}\dfrac{x^4-5x^2+4}{x^3-8}$:

• A.

  $\Large +\infty$.

• B.

  $\Large -\infty$.

• C.

  $\Large \dfrac{1}{6}$.

• D.

  1.

Chọn D.

Ta có: $\Large B=\underset{x\rightarrow 2}{lim}\dfrac{x^4-5x+4}{x^3-8}$ $\Large \underset{x\rightarrow 2}{lim}\dfrac{(x^2-1)(x^2-4)}{x^3-2^3}$ $\Large =\underset{x\rightarrow 2}{lim}\dfrac{(x^2-1)(x-2)(x+2)}{(x-2)(x^2+2x+4)}$ $\Large =\underset{x\rightarrow 2}{lim}\dfrac{(x^2-1)(x+2)}{x^2+2x+4}=1$.