Question

A building engineer analyzes a concrete column with a circular cross section. The circumference of the column is 18π meters. What is the area of the cross section?

Answer 1

Answer: 81pi square meters

--------------------------------------------------------

Work Shown

C = 18pi is the given circumference
d = diameter which is unknown

C = pi*d
18pi = pi*d
18 = d
d = 18

The diameter is 18 meters.
Half of this is the radius r = d/2 = 18/2 = 9
The radius is 9 meters

Use the value of r to find the area of the circle
A = pi*r^2
A = pi*9^2
A = pi*81
A = 81pi

The area of the circular cross section is 81pi square meters