\(\mathop {\lim }\limits_{x \to + \infty } \left( {\sqrt {{x^2} - x + 1} - x} \right) = \mathop {\lim }\limits_{x \to + \infty } \dfrac{{{x^2} + x + 1 - {x^2}}}{{\sqrt {{x^2} + x + 1} + x}} = \mathop {\lim }\limits_{x \to + \infty } \dfrac{{1 + \dfrac{1}{x}}}{{\sqrt {1 + \dfrac{1}{x} + \dfrac{1}{{{x^2}}} + 1} }} = \dfrac{1}{2}\)