Solución
$$\mathop {\lim }\limits_{x \to 1} \sqrt {f\left( x \right) - g\left( x \right)} = \root 3 \of {\mathop {\lim }\limits_{x \to 1} f\left( x \right) - \mathop {\lim }\limits_{x \to 1} g\left( x \right)} = \root 3 \of {2 + 5} = \root 3 \of 7 $$