All About Circles

What is a circle?

A circle is the set of all points in a plane; all of which are equidistant apart from a fixed point F.

Therefore an ellipse is not a circle because the points are not equidistant apart.

If this fixed point 'F', lies in the same plane as the plane of the circle then that fixed point is called the centre; if you don't know why let me tell you, if it is not in the same plane, it would be in another plane and that would make it a sphere.  

A radius is the line segment that goes from the centre. It is referred to as a A radius because there are many radii in the circle-in fact an infinite number of radii exist within the circle.

A diameter is a chord that passes through the centre of a circle. Yes I said it, a chord, it is a chord only a major one at that.

  A chord of a circle is a straight line segment whose end points lie on the circle. There exists major chords and minor chords within the circle. The chord shown below would be considered a minor chord and the diameter shown above is considered a major chord.

An arc of a circle is a portion of the circle whose length is greater than zero and less than the circumference of the circle. In case you are not understanding, it is the curved part of the circle but it must be less than the whole length of the curved part.  It is the part labelled L below on the circle.

A semi-circle is an arc of a circle whose length is half the circumference of the circle, that is, half the length of the curve portion.

A segment of a circle is the region in the circle bounded by a chord and an arc, which in the circle below would be the area shaded blue.


A sector of a circle is a region in the circle bounded by two radii and a arc.  So in the circle  below, the sector would be the area shaded in green.

That, gentlefriends is the basics of a circle. If you wish to know about solving further circle problems, write to us,