This is a soft question.
It's not difficult , say, to draw a point moving on the $y=x^2$ parabola with Desmos.
One can first declare that $b= a^2 $ , then define point $P$ as $P=(a,b) $ , and finally let vary $a$.
But this " method" does not work with the equation of a circle , first setting, say, $a^2+b^2=1$.
Any solution? Or hint?
Thanks in advance.