A circle is the locus of a point in a plane which moves such that its distance from a fixed point in the plane is always a constant.

**Circle**

The word circle is of Greek origin and reference to circles is
found as early as 1700 BC (BCE). In Nature circles would have been observed,
such as the Moon, Sun, and **ripples in water**. The circle is the basis for the wheel, which,
with related inventions such as gears, makes much of modern machinery possible.
In mathematics, the study of the circle has helped to inspire the development
of geometry, **astronomy **and calculus. In Bohr-Sommerfeld theory of the atom, **electron orbit **is modelled as circle.

**Definition 5.1**

A circle is the locus of a point in a plane which moves such
that its distance from a fixed point in the plane is always a constant.

The fixed point is called the **centre **and the constant distance is called **radius **of the circle.

Tags : Definition , 12th Mathematics : UNIT 5 : Two Dimensional Analytical Geometry II

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12th Mathematics : UNIT 5 : Two Dimensional Analytical Geometry II : Circle | Definition

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