Question

A building engineer analyzes a concrete column with a circular cross section. The circumference of the column is 18pi meters.

What is the area A of the cross section of the column?
Give your answer in terms of pi.
A = m spuared

Answer 1

Find radius

• C/2π
• 18π/2π
• 9m

So.area

• πr²
• 9²π
• 81πm²

Answer 2

• 81π m²

Explanation:

Circumference formula: C = 2πr

Compare with given value and determine the radius:

• 2πr = 18π
• r = 18π/2π
• r = 9 m

Find the area of the cross-section.

Area formula: A = πr²

Area: A = 9²*π = 81π m²