In Euclidean Geometry, a special kind of ellipse which has an eccentricity that equals zero and the two foci coincidence is called a circle. A circle can also be defined by saying that it is the figure that is traced when a locus of points are drawn at an equidistant from the center. There are many topics that students need to learn such as properties, circumference, **area of circle**, etc. Before we talk about the concepts associated with a circle we have to first understand the terms associated with it.

## Different Parts of a Circle

- Arc – A connected portion on the circumference of the circle is known as an arc
- Centre – It is a point within the circle that is at the same distance from all points lying on the circumference of the circle.
- Chord – A line segment whose endpoints are on the circle is known as a chord.
- Diameter – The longest chord of the circle that passes through the centre is called the diameter. The circle contains the endpoints of a diameter.
- Radius – A radius is half the diameter of a circle and the end points of this line segment lies on the circumference.
- Segment – The region formed between a chord and an arc is known as a segment. A point to note is that the segment never contains the center of the circle.
- Sector – The region between either of the two arcs and any two radii is called a sector.
- Semi Circle – One definition of a semicircle is the region that is bound between the diameter and one of the two arcs. It is exactly half of the circle.
- Tangent – A tangent is that line that can extend infinitely and touches a circle exactly at one single point. If there are two tangents and they touch the diameter at its end points then these two lines will always be parallel.

### Area of a Circle

We can define the area of a circle to be the entire region or space that is encompassed by the boundary of the figure. If we have the radius or diameter of a circle, then we can easily apply the given formula to find the area:

Area of a circle = pi * r^{2}, where pi is a constant that equals 3.14 or 22/7 and r is the radius

Area = pi * (d / 2)^{2}, As the diameter is equal to half of the measurement of the radius we can express the area as given above.

### Circumference of a Circle

The circle’s circumference is similar to the perimeter of a polygon. It can be defined as the complete boundary of the circle. The following formula can be used to calculate the circumference of a circle.

**Circumference = 2 * pi * r**** ****= pi * d**

For instance, what is the area and circumference of a circle with a radius of 7cm?

Solution: Radius = 7 cm

By formulas:

- Circumference = 2 * pi * r = 2 * (22/7) * 7 = 44 cm
- Area = pi * r
^{2}= (22/7) * (7)^{2}= 154 cm^{2}

##### Conclusion

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