1. Cell phone use is prohibited.
Students:
Today is a red light day.
Cell phone use is prohibited.
This is your warning.

2. Find the area. A = ½ • h • (b1 + b2) 1) 2) A = ½ • (5) • (4 + 14)
6 m
3 m
5 in
8 m
14 in
A = ½ • (5) • (4 + 14)
A = ½ • (6) • (3 + 8)
A = ½ • (5) • (18)
A = ½ • (6) • (11)
A = ½ • (90)
A = ½ • (66)
A = 45 in2
A = 33 m2
3) h = 10 , b1 = 6 , b2 = 12
4) h = 3 , b1 = 2 , b2 = 6
A = ½ • (10) • (6 + 12)
A = ½ • (3) • (2 + 6)
A = ½ • (10) • (18)
A = ½ • (3) • (8)
A = ½ • (180)
A = ½ • (24)
A = 90
A = 12

3. 17.05 Area & Circumference of a Circle

4. The center of the circle is a point.
A circle is a figure whose points are equidistant from a point in the center of the figure.
The center of the circle is a point. A •
Point A
The radius of the circle is a line that connects the center of the circle to any point on the circle.
The diameter of the circle is a line segment that connects any two points on the circle and passes thru the center.

5. The distance around a circle
is called its circumference.
Circumference Formula
C = 2 • π • r
where “r” is the radius and π = 3.14
There is another circumference formula because d = 2 • r
C = π • d
where “d” is the diameter and π = 3.14

6. Find the circumference. C = 2 • π • r or π • d
Find “r” given “d”
Find “d” given “r”
d = 16
→ r = 8
r = 13
→ d = 26
d = 9
→ r = 4.5
r = 7
→ d = 14
Find the circumference.
C = 2 • π • r or π • d
C = 2 • π • r
3 m
C = 2 • (3.14) • (3 m)
C = m or 6π m
r = 5
d = 4
C = 2 • (3.14) • (5)
C = (3.14) • (4)
C = or 10π
C = or 4π

7. The area of a circle is the number of square units needed to cover the inside of the circle.
Area Formula
A = π • r2
where “r” is the radius and π = 3.14
Find the area of the circle
r = 3
d = 8
A = 3.14 • (3)2
A = 3.14 • (4)2
A = or 9π
A = or 16π

8. Find the radius, diameter, and circumference of a circle given its area.