### Circles

```SPI 6.4.4
I CAN identify parts of a circle.
I CAN find the circumference and area of a circle.
•Circle – named from the center point.
•Radius – one endpoint at the
center; the other endpoint on
the circle
•Diameter – a segment that
passes through the center
and has both endpoints on
the circle
•Chords – endpoints on the
circle
•Central angle – an angle
with its vertex at the center.
Diameter equals 2 radius
OR
Radius is half the diameter
D = 2r
OR
Example:
r = 5 in; d = ?
D = 140 in; r = ?
R= d/2
diameter
the distance around a circle
Pi = 3.14 =
=
The ratio C = a number close to 3.
d
C = ∏d
OR
C = 2∏r
amount of surface covered
A=∏r²
OR
Ex. r = 5 cm
A= ∏xrxr
5 cm
 Find the circumference.
1)d = 50 m
2)r = 64 m
 Find the area.
3)11 in
4)16 cm
Round to the nearest whole number.
C = 5 cm
A = 2 cm²
Round to the nearest tenth.
C = 4.7 cm
A = 1.8 cm²
Diameter 1.5 cm
518.1 ft
254.34 ft
A. 9.42 in
C. 200.96 in
If the r = 7m, then d = _____, C =
_____, and A = ______.
d = 14m C = 44m
A = 154m²
If the d = 11.5 ft, then r = _____, C =
_____, and A = ______.
r = 5.75ft C = 36ft
A = 104ft²
Circumference
1.57 in
Diameter ?
d = 0.5 in
```