Tính các giới hạn sau:

\(\mathop {\lim }\limits_{x \to - \infty } \frac{{ - 3 + \frac{4}{x}}}{{2{x^2} + 3}}\);

Vì \(\mathop {\lim }\limits_{x \to - \infty } \left( { - 3 + \frac{4}{x}} \right) = \mathop {\lim }\limits_{x \to - \infty } \left( { - 3} \right) + \mathop {\lim }\limits_{x \to - \infty } \frac{4}{x} = - 3 + 0 = - 3\)

và \(\mathop {\lim }\limits_{x \to - \infty } \left( {2{x^2} + 3} \right) = \mathop {\lim }\limits_{x \to - \infty } \left[ {{x^2}\left( {2 + \frac{3}{{{x^2}}}} \right)} \right] = \mathop {\lim }\limits_{x \to - \infty } {x^2}.\mathop {\lim }\limits_{x \to - \infty } \left( {2 + \frac{3}{{{x^2}}}} \right) = + \infty \).

Do đó, \(\mathop {\lim }\limits_{x \to - \infty } \frac{{ - 3 + \frac{4}{x}}}{{2{x^2} + 3}} = 0\).