Past exam of the mathematics course of the University of Cambridge / 2023 / ia / Paper 2 / 8A / b / iii / Solution

The sign of $\dot{x}$ is the sign of $y$. The $\dot{y}=0$ nullcline is$\dot{y}$ is positive below this curve and negative above it. Combining the upper and lower half-planes with the regions above and below this even curve labels the four requested sign combinations.