Area & Circumference of Circles

Front

What is the formula for the area of a circle?

Back

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

Front

What is the formula for the circumference of a circle?

Back

C = 2πr or C = πd, where C is the circumference, r is the radius, and d is the diameter.

Front

If the radius of a circle is 5 inches, what is the area?

Back

A = π(5)² = 25π ≈ 78.5 in².

Front

If the diameter of a circle is 10 inches, what is the circumference?

Back

C = πd = π(10) ≈ 31.4 in.

Front

What is the relationship between diameter and radius?

Back

The diameter is twice the radius: d = 2r.

Front

How do you find the radius if you know the circumference?

Back

r = C / (2π).

Front

What is the area of a circle with a radius of 7 cm?

Back

A = π(7)² = 49π ≈ 153.94 cm².

Front

What is the circumference of a circle with a radius of 3 m?

Back

C = 2π(3) = 6π ≈ 18.85 m.

Front

If a circle has a circumference of 20π, what is its diameter?

Back

d = 20 inches.

Front

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

Back

A = π(6)² = 36π ≈ 113.1 in².