The area of a circle is
and the perimeter or circumference is
A sector is a fraction of a circle.
To find the area of a sector, we just find that fraction of the area of a circle.
The sector to the right is a fraction
of the circle to the left so the the area of the sector is
The curved part of the sector isof the circumference of the circle but to find the perimeter of the sector we must add
(the radius of the circle is
) so the perimeter of the sector is
If
and
the area of the sector is
and the perimeter is