5.1 Sector Intro
The AREA of a circle
can be found using
which formula?
2∏r
 ∏r2
SECTOR = part of the AREA
A SECTOR of a circle
is part of the AREA
of the circle.
SECTOR = part of the AREA
A             of a circle
is part of the
of the circle.
sector
?
area
?
180
SECTOR = part of the AREA
A full circle is           degrees...
How large is the part ??
The angle measure of a full circle (360)
Place the sector angle (central angle)
OVER
180
SECTOR = part of the AREA
A full circle is 360 degrees.
How large is the part ??
180
?
360
?
360
180
180
=
18
36
Reduce 180/360

to find what part
of the area the sector is.
=
180
A 180 degree sector
is exactly one half
the AREA of a circle.

If the AREA of this circle
was 42∏, the 180 degree
SECTOR area would be
half of that,         ∏
A 120 degree sector
is what part (fraction)
of the full circle?
 ½
 ⅓
¼
1/5
120
360
=
12
36
=
A 120 degree sector
is what part (fraction)
of the full circle?
1
3
 ⅓
A 90 degree sector
is what part (fraction)
of the full circle?
 ½
 ⅓
¼
1/5
360
90
=
36
9
=
A 90 degree sector
is what part (fraction)
of the full circle?
1
4
¼
A 60 degree sector
is what part (fraction)
of the full circle?
 1/4
 1/5
1/6
6/6
360
60
=
36
6
=
A 60 degree sector
is what part (fraction)
of the full circle?
1
6
1/6
Full Circle angle measure
Central sector angle
72
A 72 degree sector
is what part of the
full circle?
360
?
72
?
=
360
72
=
1
5
6cm
SECTOR= Part  of  the  AREA
sector angle
360
360
*
*
∏    2
∏r2
reduce the fraction
6cm
SECTOR= Part  of  the  AREA
sector angle
360
360
90
*
*
*
∏62
∏r2
=
The 90 degree sector equals 9∏ cm2
The total AREA is       ∏ cm2
9∏
9∏
9∏
9∏
6cm
SECTOR= Part  of  the  AREA
sector angle
360
360
*
*
∏    2
∏r2
reduce the fraction
6cm
SECTOR= Part  of  the  AREA
sector angle
360
360
120
*
*
*
∏62
∏r2
=
The 120 degree sector equals 12∏ cm2
The total AREA is       ∏ cm2
12∏
12∏
12∏
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