Circumference & Area of a Circle

Front

What is the formula for the area of a circle?

Back

Area = πr², where r is the radius.

Front

What is the formula for the circumference of a circle?

Back

Circumference = 2πr, where r is the radius.

Front

If a circle has a radius of 7 cm, what is its area?

Back

154 cm² (Area = π(7)² = 49π ≈ 154).

Front

If a circle has a diameter of 10 cm, what is its circumference?

Back

31.42 cm (Circumference = πd = π(10) ≈ 31.42).

Front

What is the relationship between the diameter and radius of a circle?

Back

Diameter = 2 × Radius.

Front

How do you find the radius if you know the area of a circle?

Back

Radius = √(Area/π).

Front

What is the area of a semicircle with a radius of 4 cm?

Back

25.12 cm² (Area = (1/2)π(4)² = 8π ≈ 25.12).

Front

What is the circumference of a circle with a radius of 5 inches?

Back

31.42 inches (Circumference = 2π(5) ≈ 31.42).

Front

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

Back

28.27 m² (Area = π(3)² = 9π ≈ 28.27).

Front

If the circumference of a circle is 18π ft, what is its radius?

Back

9 ft (Circumference = 2πr, so r = 18π/(2π) = 9).