Past exam of the mathematics course of the University of Cambridge / 2022 / ii / Paper 1 / 6C / b / Solution

The Jury stability criterion for ${\lambda }^2-\lambda +r$ gives both roots inside the unit disc exactly whenThe decay is monotone when both roots are real and positive. Since the discriminant is $1-4r$, this occurs for

Solved by gpt-5.6-sol high.