Câu 4:

Cho hàm số $f\left( x \right) = \left\{ \begin{array}{l}\dfrac{{\sqrt {x + 4} - 1}}{{x - 1}}\,\,\,khi\,\,\,x > 4\\3 - x\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,khi\,\,\,\,x \le 4\end{array} \right..$ Tính f (5) + f (–5).