Question

Henry know that the circumference of a circle is 18 pie inches. What is the area of the circle?

A:36
B:81
C:162
D:324

Answer 1

B. 81

Explanation:

Answer 2

B: 81π inches

Explanation:

The formula for the circumference of a circle is C = πd and the formula for the area of a circle is A = πr²

• The formula for the circumference of a circle can also be written as C = 2πr since the diameter is equal to double the radius (d = 2r)
• So we need to solve for r since that is the variable we are missing in order to solve for the area

Plugging in our known values to the circumference formula we have:

• 18π = 2πr
• Then dividing both sides by 2π we have 9 = r

Now that we have solved for the radius, we can plug in this value to the area formula:

• A = π(9)² = 81π in