Bridgette measured a manhole cover and calculated that its circumference is 6.28 feet. What is the manhole cover's area?

Question

I don't know how to do the circumference when you have to find the area.

Answer 1

circumference = 6.28 feet = pi(d) = 2pi(r) where d= diameter and r= radius

2pi(r) = 6.28

pi(r) = 3.14

pi= approximately 3.14

3.14(r) = 3.14

r = 3.14/3.14 = 1

area = pi(r^2) = pi(1^2) = pi = 3.14

area = approximately 3.14 square feet

in general, circumference = 2pi(r)= C

pi(r) = C/2

area = pi(r)^2 = A

pi(r) = A/r

A/r = C/2

A = rC/2

if C=6.28, r= 1, then

A= (1)(6.28)/2 = (6.28)/2 = 3.14

Area = 3.14