CIRCLES
Circles have many different parts to them:
-the
circumference
-the area
-an
arc
-a
sector
-and a
segment
In all circles, the ratio of the diameter to the circumference is
approximately 3.14159, symbolized by the Greek letter pi. To find the
circumference of a circle, multiply the diameter by pi, or if you are just
given the radius, double the radius and multiply that by pi, because
the length of the diameter is twice the length of the radius.
The area of a circle is the space contained by the circumference. To
find the area of a circle, multiply pi by the square of the radius. Or,
if you are only given the circumference, multiply the circumference by
the radius and divide the product by two. The area is always written in
square units.
An arc is a curved portion of a circle. The relationship of its length
to the circumference is proportional to the relationship of the angle
formed by the radii of the arc to the total angle of the circle at the
center. To find the
arc length, divide the degree measure of the central angle by 360
and multiply the quotient by the circumference,
or 2*pi*r.
A sector is the pie-shaped piece of the circle "cut out" by two radii.
The ratio of the area of the sector to the area of the circle is equal
to the ratio of the arc length of the sector to the circumference, which
is the same as the ratio of the angle of the sector to the total angle of
the circle.
A segment is either of the two regions into which a line or line segment cuts
a circle.
Some
Examples
Practice
Problems