Assertion: ellipse's property | /r/HasProperty | proved
Facets:
value: easily
type: MANNER
value: from the focal definition
type: OTHER
Source sentences:
text: This property (which can be proved using the Dandelin spheres) can be taken as another definition of the ellipse.
text: The property that the sum of the radii from the foci to a point on the ellipse is constant is easily derived from the focal definition, as shown in the figure.