The canonical equation of the ellipse is x² / a² + y² / b² = 1, a>=b.
Ellipse x² / a² + y² / b² = 1 can be described by comparing with the circle of radius a centered at the center of the ellipse.
For each x such that abs(x)<=a , there are two points E, D on the ellipse, and two points A, C on the circle.
The ratio of ordinates of the points E, A and D, C is equal to b/a.
The ellipse is obtained from the circle by compressing it to the horizontal axis, the coordinates decrease in the same ratio b/a.
Proposition 1
The axes of the canonical coordinate system are the symmetry axes of the ellipse
x² / a² + y² / b² = 1, and the origin of the coordinate system is its center of symmetry

Supplementary problems
1) Create point O as intersection of X-axis and Y-axis;
2) Show that the point O is the center of symmetry.