$\begin{array}{l}\mathop {\lim }\limits_{x \to a} f(x) = \mathop {\lim }\limits_{x \to a} {x^2} + \mathop {\lim }\limits_{x \to a} x - 7 = {a^2} + a - 7\\ =  - 1 \Rightarrow {a^2} + a - 6 = 0\\ \Rightarrow (a + 3)(a - 2) = 0\\ \Rightarrow \left\{ {\begin{array}{*{20}{c}}{a =  - 3}\\{a = 2}\end{array}} \right.\end{array}$ دامنه $ = \left[ {0,3} \right] \Rightarrow a = 2$