Chapter 3 - Quadratic Functions - 3.2 The Vertex of a Parabola - Exercises and Problems for Section 3.2 - Exercises and Problems - Page 128: 26

See below.

Use the discriminant value. The discriminant is equal to $b^2-4ac$. The value of the discriminant is $$(-1)^2-4(1)(41)=1-164=-163$$ This is negative, meaning that the quadratic formula contains the square root of a negative. This forces all the roots to be imaginary.