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An ellipse is a closed curve where the sum of the distances to the two foci is:
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CA constant
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Answer & Solution
Correct answer: C. A constant
1. An ellipse can be drawn with a string looped around two pins.
2. The string length never changes as the pencil moves.
3. The sum of the distances from a point on the curve to the two foci is a constant.
4. That is what makes the curve an ellipse rather than a circle.
_Source: OpenStax College Physics for AP Courses 2e (CC BY 4.0), Ch 6 'Uniform Circular Motion and Gravitation', sections 6.1-6.6_
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