\(\mathop {\lim }\limits_{y...

C

- Hướng dẫn giải

\(\begin{array}{l}
\mathop {\lim }\limits_{y \to a} \frac{{{y^4} - {a^4}}}{{y - a}} = \mathop {\lim }\limits_{y \to a} \frac{{\left( {y - a} \right)\left( {y + a} \right)\left( {{y^2} + {a^2}} \right)}}{{y - a}}\\
 = \mathop {\lim }\limits_{y \to a} \left( {y + a} \right)\left( {{y^2} + {a^2}} \right) = 4{a^3}
\end{array}\)