Parametric Curve(s)
$$$ \left \{ \begin{array}{r c l} \theta(\alpha)& = &\alpha \\ r(\alpha)& = &a\times\left (\sin^{2.9}{(0.5\cdot\alpha)}\right )-b \end{array}\right .$$$
$$$ \left \{ \begin{array}{r c l} \theta(\alpha)& = &\alpha \\ r(\alpha)& = &a\times\left (\sin^{2.9}{(0.5\cdot\alpha)}\right )-b \end{array}\right .$$$