Page 10 - CONIC SECTION - EBOOK._Neat
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Conic section
ELLIPSE
An ellipse, informally, is an oval or a "squished" circle. In "primitive"
geometrical terms, an ellipse is the figure you can draw in the sand by the
following process: Push two sticks into the sand. Take a piece of string and
form a loop that is big enough to go around the two sticks and still have some
slack. Take a third stick, hook it inside the string loop, pull the loop taut by
pulling the stick away from the first two sticks, and drag that third stick
through the sand at the furthest distance the loop will allow. The resulting
shape drawn in the sand is an ellipse.
Each of the two sticks you first pushed into the sand is a "focus" of the ellipse;
the two together are called "foci" (FOH-siy). If you draw a line in the sand
"through" these two sticks, from one end of the ellipse to the other, this will
mark the "major" axis of the ellipse. The points where the major axis touches
the ellipse are the "vertices" of the ellipse. The point midway between the
two sticks is the "center" of the ellipse.
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