Circumference and Area of a Circle

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

What is the formula for the area of a circle?

Back

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

Front

If the radius of a circle is 10 mm, what is its circumference?

Back

C = 2π(10) ≈ 62.83 mm.

Front

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

Back

A = π(5)² ≈ 78.54 cm².

Front

How do you convert diameter to radius?

Back

Divide the diameter by 2.

Front

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

Back

Diameter = 2 × radius = 2 × 7 = 14 cm.

Front

What is the value of π (pi) approximately?

Back

π ≈ 3.14.

Front

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

Back

Radius = C / (2π) = 31.4 / (2π) ≈ 5 cm.

Front

What is the area of a circle with a diameter of 8 cm?

Back

Radius = 8 / 2 = 4 cm; A = π(4)² ≈ 50.27 cm².

Front

What happens to the area of a circle if the radius is doubled?

Back

The area increases by a factor of 4 (A = π(2r)² = 4πr²).