Circumference and Area of Circles

Front

What is the formula for the circumference of a circle?

Back

C = 2πr, where C is the circumference and r is the radius.

Front

How do you calculate the area of a circle?

Back

A = πr², where A is the area and r is the radius.

Front

If the diameter of a circle is known, how can you find the radius?

Back

The radius is half of the diameter (r = d/2).

Front

What is the relationship between circumference and diameter?

Back

The circumference is π times the diameter (C = πd).

Front

How do you convert circumference to radius?

Back

r = C / (2π).

Front

What is the area of a circle with a radius of 5 feet?

Back

A = π(5)² = 25π ≈ 78.54 ft².

Front

If a circle has a circumference of 31.4 cm, what is its diameter?

Back

d = C / π = 31.4 / π ≈ 10 cm.

Front

What is the circumference of a circle with a radius of 10 inches?

Back

C = 2π(10) = 20π ≈ 62.83 inches.

Front

How do you find the area of a circle if you only have the circumference?

Back

First, find the radius using r = C / (2π), then use A = πr².

Front

What is the area of a circle with a diameter of 12 cm?

Back

A = π(6)² = 36π ≈ 113.10 cm².