Assertion: ellipse's point | /r/CreatedBy | the locations of the two tacks
Facets:
Source sentences:
text: The coordinates of the focal points are: \[ F_1 = (-e,0), \qquad F_2 = (e,0), \] where $e=\sqrt{a^2 - b^2}$. The focal points correspond to the locations of the two tacks where the string is held fixed.