Giải thích các bước giải:
$\lim_{x\to-1^-}\dfrac{1}{-x^2+x+2}-\dfrac{2}{x^3+1}$
$=\lim_{x\to-1^-}\dfrac{1}{-(x-2)(x+1)}-\dfrac{2}{(x+1)(x^2-x+1)}$
$=\lim_{x\to-1^-}\dfrac{1}{x+1}(\dfrac{1}{-(x-2)}-\dfrac{2}{x^2-x+1})$
$=-\dfrac{1}{-1+1}(\dfrac{1}{-(-1-2)}-\dfrac{2}{(-1)^2-(-1)+1})$
$=-\infty.(-\dfrac 13)$
$=+\infty$