چون f در R پیوسته است، پس تابع $f(x)$ در $x = - 1$ نیز پیوسته است، بنابراین:
$\mathop {\lim }\limits_{x \to {{( - 1)}^ - }} f(x) = \mathop {\lim }\limits_{x \to {{( - 1)}^ + }} f(x) = f( - 1)$
$\left. {\begin{array}{*{20}{c}}
{\mathop {\lim }\limits_{x \to {{( - 1)}^ - }} f(x) = \mathop {\lim }\limits_{x \to {{( - 1)}^ - }} (3 - {x^2}) = 2}\\
{\mathop {\lim }\limits_{x \to {{( - 1)}^ + }} f(x) = \mathop {\lim }\limits_{x \to {{( - 1)}^ + }} x + a = - 1 + a}
\end{array}} \right\} \Rightarrow 2 = - 1 + a \Rightarrow a = 3$
$\mathop {\lim }\limits_{x \to {2^ + }} f(x) = \mathop {\lim }\limits_{x \to {2^ + }} (x + a) = 2 + a\,\,\underline{\underline {a = 3}} \,\,2 + 3 = 5$