**8.2: The Ellipse - Mathematics LibreTexts**
https://math.libretexts.org/Bookshelves/Algebra/College_Algebra_1e_(OpenStax)/08%3A_Analytic_Geometry/8.02%3A_The_Ellipse

WebOct 6, 2021 · An ellipse is the set of all points \((x,y)\) in a plane such that the sum of their distances from two fixed points is a constant. Each fixed point is called a focus(plural: foci). We can draw an ellipse using a piece of cardboard, two thumbtacks, a pencil, and string. Place the thumbtacks in the cardboard to form the foci of the ellipse.

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