Circle Properties 2
A circle is a plane figure bounded by one curved line, every point of which is equally distant from a certain point within, which is called its center.
Definitions related to circles:
Arc: A continuous piece of a circle is called an arc. In other words, any portion of the circumference of a circle is called an arc.
Chord: A straight line joining any two points on the circumference of a circle is called a chord.
Circumference: The perimeter of a circle is called its circumference
Diameter: Any straight line drawn through the centre and terminating at both ways by the circumference is called a diameter.
Origin: Origin refers to the center of a circle
Pi ( 
): An approximate value of is 22/7 which is correct to two decimal places. A more accurate value of is 3.14159 which is correct to five decimal places.
Radius: The constant distance of every point on the circle from its centre is called the radius of the circle. It is half of the diameter.
Sector: A sector is that part of a circle, which lies between an arc and two radii joining the extremities of the centre. The most important sector is a quadrant, which is one-fourth of the circle.
Tangent of a circle: It is a line perpendicular to the radius that touches only one point on the circle.
Circumference of a circle: = 2 r where is 22/7 or 3.14159
Area of a circle = r2
Length of a Circular Arc: (with central angle 
)
- if the angle is in degrees, then length = x (/180) x r
- if the angle is in radians, then length = r x
Area of Circle Sector: (with central angle )
- if the angle is in degrees, then area = (/360) x r2
- if the angle is in radians, then area = [(/(2)] x r2
If you feel you're ready, try the circle test.