Tính giới hạn sau

a) \[\mathop {\lim }\limits_{n \to + \infty } \frac{{3{n^3} - 2{n^2} + 4}}{{ - 2{n^3} + 5n - 1}} = \mathop {\lim }\limits_{n \to + \infty } \frac{{3 - \frac{2}{n} + \frac{4}{{{n^3}}}}}{{ - 2 + \frac{5}{{{n^2}}}n - \frac{1}{{{n^3}}}}} = - \frac{3}{2}\]

b) \(\mathop {\lim }\limits_{x \to - 2} \frac{{3{x^2} + 5x - 2}}{{4 - {x^2}}} = \mathop {\lim }\limits_{x \to - 2} \frac{{\left( {x + 2} \right)\left( {3x - 1} \right)}}{{\left( {2 - x} \right)\left( {2 + x} \right)}}\)\( = \mathop {\lim }\limits_{x \to - 2} \frac{{\left( {3x - 1} \right)}}{{\left( {2 - x} \right)}} = \frac{{ - 7}}{4}\)