### Liénard system

Let us consider the following Liénard system corresponding to a perturbation of a weak focus [Perko (2001)]:

\begin{equation*}
\begin{cases}
\dot{x} = y + \varepsilon p(x) \\
\dot{y} = -x,
\end{cases}
\end{equation*}

where the perturbation function \(p\) is given by:
\begin{equation*}
p(x) = 72 x - \dfrac{392}{3} x^3 + \dfrac{224}{5} x^5 - \dfrac{128}{35} x^7 .
\end{equation*}

You can visualize the phase portrait of the perturbed system: choose a value of \(10\varepsilon\) (decimal number between \(0\) and \(1\)).
For \(\varepsilon > 0 \) sufficiently small, the system presents 2 stable limit cycles and 1 unstable limit cycle.