Final answer:
The equation 'y = 4x² + 1' is not linear because it is a quadratic equation. Linear equations are in the form 'y = mx + b' and do not include variables raised to a power higher than one.
Step-by-step explanation:
The equation that represents a function that is NOT linear is y = 4x² + 1. This is because it contains an x raised to the second power (x^2), which makes it a quadratic equation. A linear equation is represented in the form y = mx + b, where m and b are constants, and the graph of a linear equation is a straight line.
The other equations provided, y = 2x - 1, y = (1/2)x - 2, and y = -5, are all linear because they can be rewritten in the form of y = mx + b without any exponents on x. Therefore, these equations would produce straight lines when graphed, as opposed to the curve produced by the quadratic equation.