LIm căn {{x^2} - 5x + 7} + x} bằng9/39\(\mathop {\lim }\limits_{x \to - \infty } \left( {\sqrt {{x^2} - 5x + 7} + x} \right)\) bằng\( - \infty \)\( - \frac{5}{2}\)\(\frac{5}{2}\)\( + \infty \)Giải thíchChọn C