Circles Definition and 310 Threads

A circle is a shape consisting of all points in a plane that are at a given distance from a given point, the centre; equivalently it is the curve traced out by a point that moves in a plane so that its distance from a given point is constant. The distance between any point of the circle and the centre is called the radius. This article is about circles in Euclidean geometry, and, in particular, the Euclidean plane, except where otherwise noted.
Specifically, a circle is a simple closed curve that divides the plane into two regions: an interior and an exterior. In everyday use, the term "circle" may be used interchangeably to refer to either the boundary of the figure, or to the whole figure including its interior; in strict technical usage, the circle is only the boundary and the whole figure is called a disc.
A circle may also be defined as a special kind of ellipse in which the two foci are coincident and the eccentricity is 0, or the two-dimensional shape enclosing the most area per unit perimeter squared, using calculus of variations.

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  1. F

    Finding Tangent Lines to Two Circles

    How do you find the equation of the (sometimes 2 possible) tangent lines between two (or more) circles? like the 2 tangents that cross in the picture on this page: http://mathworld.wolfram.com/Circle-CircleTangents.html. The application for this is for a program that would draw this tangent...
  2. R

    Area of circle inscribed with 3 smaller circles

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  3. murshid_islam

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  4. B

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  5. J

    Does the Higgs field explain anything or go in circles?

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  6. M

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  7. A

    How Do You Determine Capacitance from a ln(r) vs V Graph?

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  8. J

    Geometry of circles and polygons.

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  9. B

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  10. R

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  11. andrewkirk

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  12. B

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  13. D

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  14. F

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  15. G

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  16. D

    Geometry Homework: Sum of Circles and Triangles in Figure

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  17. D

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  18. binbagsss

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  19. binbagsss

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  20. X

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  21. nicksauce

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  22. R

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  23. M

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  24. T

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  25. DaveC426913

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  26. C

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  27. S

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  28. H

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  29. M

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  30. M

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  31. C

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  32. Z

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  33. wolram

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  34. F

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  35. P

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  36. A

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  37. R

    How many circles can be placed inside another circle?

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  38. B

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  39. M

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  40. X

    Parametric equations and finding tangents from circles

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  41. S

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  42. E

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  43. C

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  44. K

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  45. T

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  46. S

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  47. P

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  48. L

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  49. M

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  50. C

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