Question

Circle A has a diameter of 8 inches, a circumference of 25.12 inches, and an area of 50.24 square inches. The diameter of circle B is 3 inches, the circumference is 9.42 inches, and the area is 7.065 square inches.

Part A: Using the formula for circumference, solve for the value of pi for each circle. (4 points)

Part B: Use the formula for area and solve for the value of pi for each circle. (4 points)

Part C: What observation can you make about the value of pi for circles A and B? (2 points)

help?

Answer 1

it says "Using the formula for circumference, "

Do you know the formula for find the circumference of a circle ?

Answer 2

yeah

Answer 3

what is it ?

Answer 4

c=3.14r squared

Answer 5

almost. it's not 3.14

Answer 6

ooo

Answer 7

hold on

Answer 8

also, that is the formula for the area.
you want the formula for the circumference.

Answer 9

2(3.14)r

Answer 10

It's a famous formula.
\[ C= 2 \pi r \]
we use the Greek letter \( \pi\) because if we tried to write out the actual number, it goes on forever.

Answer 11

in other words, 3.14 is just "roughly" the actual value of pi

now they say
Circle A has a diameter of 8 inches
what is the radius of circle A? any idea ?

Answer 12

ok, except use pi instead of 3.14
pi * 8 = 25.12
now "solve for pi" by dividing both sides by 8
pi= 24.12/8
what do you get ?

Answer 13

you get pi= 24.12/8 = 3.24
and if you do the same for circle B:
pi * 3= 9.42
pi = 9.42/3 = 3.14
so you get the same number for both circles. That is part 1

Answer 14

*part A

for part B, write down the formula for the area of a circle (and use pi)

Answer 15

A= pi r^2

now put in the area for circle A 50.24
and the radius (it is 4)
50.24= pi * 4*4
or
50.24= pi * 16
solve for pi (divide both sides by 16)

Answer 16

can you do the same for the other circle (using its area) ?

Answer 17

Part B: Use the formula for area and solve for the value of pi for each circle. (4 points)

Answer 18

this question is different from what you did.
they want you to "solve for pi" using the info that the area of circle B is 7.065 square inches.
also, they give you B's diameter as 3. you need B's radius

Answer 19

you start with
\[ A = \pi r^2\]
put in 7.065 for the area (replace A with that number)
also, put in the radius
then "solve for pi"

Answer 20

the radius is 1/2 of 3
or 3/2
or 1.5

Answer 21

in other words, they told you the diameter is 3, so you know the radius is half of that

Answer 22

put in 7.065 for the area (replace A with that number) also, put in the radius then "solve for pi"

Answer 23

we are doing part B
Part B: Use the formula for area and solve for the value of pi for each circle.

for circle A you did
A= pi r^2
now put in the area for circle A 50.24 and the radius (it is 4)
50.24= pi * 4*4 or
50.24= pi * 16 solve for pi (divide both sides by 16)
pi = 50.24/16 = 3.14
we found pi is 3.14 for circle A

now we are doing circle B
A= pi r^2
put in the area for circle B 7.065 and the radius (it is 1.5)

Answer 24

can you show your work ?

Answer 25

ok, but the formula is
7.065 = pi * (1.5)^2
1.5^2 means 1.5*1.5

Answer 26

so pi*1.5*1.5=7.065 right?