1. HW: Circumference & Area Wkst #2 (show all algebra)
Wednesday, 3/22/17
Write the IC and HW in your planner.
IC: Ch. 8 Circles – day 5
HW: Circumference & Area Wkst #2 (show all algebra)
Materials
Pencil/Grading pen
Slate/marker/eraser
Math folder
Circumference & Area Wkst
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2. Bellwork red green blue red 1st Pick 2nd Pick 1st Pick 2nd Pick x = x
Problem:
What is the probability of choosing a red jolly rancher first and then a green?
Example:
What is the probability of choosing a blue jolly rancher and then a red jolly rancher?
red
green
blue
red
1st Pick 2nd Pick
1st Pick 2nd Pick x = x =

3. Bellwork green blue blue red 1st Pick 2nd Pick 1st Pick 2nd Pick x = x
Problem:
What is the probability of choosing a green first, putting it back, and then picking a blue?
Example:
What is the probability of choosing a blue lollipop, putting it back, and then picking a red?
green
blue
blue
red
1st Pick 2nd Pick
1st Pick 2nd Pick x = x =

4. d = 2 cm d = 4 cm d = 10 cm d = 75 cm Circle Approximate Circumference
More Precise Circumference
Precise! Exact! No rounding!
d = 2 cm
d = 4 cm
d = 10 cm
d = 75 cm
C  3d
C = d
C = d
C  3(2)
C  (3.14)(2)
C = (2)
C  6 cm
C  6.28 cm
C = 2 cm
C  3d
C = d
C = d
C  3(4)
C  (3.14)(4)
C = (4)
C  12 cm
C  cm
C = 4 cm
C  3d
C = d
C = d
C  3(10)
C  ( )(10)
C = (10)
C  30 cm
C  cm
C = 10 cm
C  3d
C = d
C = d
C  3(75)
C  (3.14)(75)
C = (75)
C  225 cm
C  cm
C = 75 cm

5. Circumference and Area of Circles
Determine the _____________
Choose and write the ____________
___________________ the variables into the formula
_____________
STEPS
variables
formula
Substitute
Solve
Label

6. 5 in = d 2.5 in = r 15.7 in d = 5 19.625 in² r = 2.5 r = A = ½ C • r
Example 2:
Circumference = _________
Area = __________
d = 5
in²
r = 2.5
r =
A = ½ C • r
C =  d
A = ½ (15.7)• 2.5
C = 3.14(5)
A = 7.85 (2.5)
C = 15.7 in
A = in²
5 in = d
2.5 in = r

7. Time for Word Problems! 2.5 ft A = ½ C • r d 3.14(5) A = ½ ( )• 2.5
AREA
Cover
Time for Word Problems!
CIRCUMFERENCE
Around
Example 5: A round table has a radius of 2.5 feet and you need to protect it. (It’s an antique.) How much glass do you need to cover the table to keep it pristine?
Area or Circumference?
Draw a picture:
A = ½ C • r d
3.14(5)
A = ½ ( )• 2.5
15.7
2.5 ft
= 7.85 (2.5)
r = 2.5
ft² of glass
d = 5
d =

8. Example 8: A round spa has tile that goes around the edge
Example 8: A round spa has tile that goes around the edge. How many feet is it to go all the way around the spa if the diameter is 8 feet?
Area or Circumference?
Draw a picture:
C = d
C ≈ 3.14(8)
C ≈ 25.12
8 ft
It is feet to go all the way around.
d = 8
r = 4
r =

9. Archimedes
B.C.

10. Archimedes was a mathematician, physicist, engineer, inventor, and astronomer.
He is credited with deriving an accurate approximation of the concept of pi.

11. Archimedes invented a unique way to move water uphill.
This technology was also used to get water out of the hull of a ship that had developed a leak or had taken on water.

12. Archimedes invented a way to light attacking ships on fire using mirrors to focus the energy of the sun.

13. Archimedes invented a way to lift an attacking ship out of the water to the point that they take on water and then drop it back in to sink.

14. One theory of the death of Archimedes states that he was killed during the siege of the city he was living in by a invading Roman soldier.

15. 0.4 m 2.512 m 0.5024 m² A = ½ C • r A = ½ (2.512)• 0.4 C =  d
Example 3:
Circumference = _________
Area = __________ m²
A = ½ C • r
0.4 m
A = ½ (2.512)• 0.4
C =  d
A = (0.4)
C = 3.14(0.8)
C = m
A ≈ m²
r = 0.4
d = 0.8
d =