Question

How is the circumference of a circle with radius 9cm related to the circumference of a circle with diameter 9cm?
i don't understand this.Help?? Thanks:)

Answer 1

Start with the equation of circumference of a circle:

c = pi x d.

The diamter is 2 x radius. So, the diameter of the first cirlce is 18cm. You know the diameter of the second circle. So, how do the circumferences compare?

Answer 2

is the second circle twice as big? like is that how they compare?

Answer 3

the circumference of the larger circle is indeed twice as long as that of the smaller one.

but...
the area of the larger circle is 4 times that of the area of the smaller.

Proof:
area of smaller = pi(4.5)^2 = 20.25pi
area of larger = pi(9^2) = 81pi

20.25pi/(81pi) = 1/4

Answer 4

alright thx!