On the distribution and number of limit cycles for quadratic systems with two foci (Q1431480)

This paper deals with quadratic systems with two foci, which without loss of generality can be written in the form \[ {dx\over dt} -y+\delta x+ tx^2+ mxy+ y^2= P(x,y),\quad {dy\over dt} = x(1+ ax+ by)= Q(x,y),\tag{1} \] with \(a\geq 0\) and \(1+ b< 0\). The main goal of the paper is to prove the following result: a quadratic system (1) has at most one limit cycle surrounding one of its two foci.