Phase portraits of some polynomial differential systems with maximal multiplicity of the line at the infinity

The present study delves into the investigation of phase portraits of polynomial differential systems, which are systems of differential equations of the form $\frac{dx}{dt} = P(x,y), \frac{dy}{dt} = Q(x,y)$, where $x$ and $y$ are the dependent variables and $t$ is the independent variable. The functions $P(x,y)$ and $Q(x,y)$ are polynomials in $x$ and $y$. The main objective of this research is to obtain the phase portraits of polynomial differential systems of degree $n\in \{ 3, 4, 5\}$ and having an invariant straight line at the infinity of maximal multiplicity.