Circles: Circumference and Area

Front

What is the formula for the circumference of a circle?

Back

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

Front

If the diameter of a circle is 15 mm, what is the radius?

Back

7.5 mm

Front

What is the relationship between diameter and radius?

Back

The diameter is twice the radius (d = 2r).

Front

How do you calculate the area of a circle?

Back

A = πr², where r is the radius.

Front

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

Back

c = 2π(10) = 20π ft.

Front

If the radius of a circle is 9, what is the area?

Back

A = π(9)² = 81π.

Front

What is the diameter of a circle with a radius of 18?

Back

36.

Front

What is the circumference of a circle with a diameter of 3 cm?

Back

c = π(3) ≈ 9.42 cm.

Front

What does π (pi) represent in circle calculations?

Back

π is a constant approximately equal to 3.14, representing the ratio of the circumference to the diameter of a circle.

Front

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

Back

d = c/π = 31.4/π ≈ 10 ft.