Circumference and Area of Circles

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 10 cm, what is the radius?

Back

5 cm

Front

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

Back

A = πr² = 9π square cm.

Front

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

Back

Diameter (d) = 2 × Radius (r).

Front

What is the relationship between diameter and circumference?

Back

Circumference (C) = π × Diameter (d).

Front

If a circle has a radius of 7 meters, what is its circumference?

Back

C = 2π(7) = 14π meters.

Front

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

Back

A = πr² = π(6)² = 36π square feet.

Front

If the circumference of a circle is 31.4 meters, what is the radius?

Back

r = C/(2π) = 31.4/(2π) = 5 meters.

Front

What is the formula for the area of a circle?

Back

A = πr², where r is the radius.

Front

If the radius of a circle is doubled, how does the area change?

Back

The area increases by a factor of 4.