Hello!
We must use a certain formula to find the circumference of a circle. The formula is:
C = 2 × pi × r
We have the diameter of the circle, so we'll be able to find its radius, since radius is always half the diameter.
r = d ÷ 2
r = 9 ÷ 2
r = 4.5
So, the radius of the circle is 4.5 centimetres. Pi equals approximately 3.14. Substitute:
C = 2 × 3.14 × 4.5
C = 6.28 × 4.5
C = 28.26
ANSWER:
The circumference of the circle is 28.26 centimetres long.