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A detailed tutorial on eccentricity. Step by step tutorial including sample problems and a visual representation of eccentricity for reference.

Eccentricity is a parameter associated with every conic section. Another way to think of it is as a measure of how much the conic section deviates from being circular. Each shape has a different eccentricity. The eccentricity of a circle is zero – because it does not deviate at all from being circular. The eccentricity of an ellipse that is not a circle is less than one but greater than zero, because it is almost a circle. The eccentricity of a parabola is one, and the eccentricity of a hyperbola is greater than one. Eccentricity plays an important part in calculations because two conic sections are only similar if they have the same eccentricity.

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A detailed tutorial on the solving for the foci of an ellipse. Step by step tutorial including several examples of how to solve for the Foci of an Ellipse for reference.

An ellipse has two points called foci.  From these two points, a line can be drawn to any point on the circle and the sum of the distance from each focus to the point will equal 2 times the major radius.

Where is the minor radius, is the distance from the first focus to the point, and is the distance from the second focus to the point. To find the focis use the formula:

Where is the major radius and is the minor radius.