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

What is the formula for the area of a circle?

Back

A = πr², where r is the radius.

Front

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

Back

C = 2π(7) ≈ 43.98 cm.

Front

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

Back

A = π(5)² ≈ 78.54 cm².

Front

What is the relationship between diameter and radius?

Back

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

Front

How do you convert diameter to radius?

Back

Divide the diameter by 2 (r = d/2).

Front

What is the circumference of a circle with a radius of 13.5 mm?

Back

C ≈ 84.78 mm.

Front

What is the area of a circle with a radius of 9 cm?

Back

A ≈ 254.47 cm².

Front

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

Back

r = C/(2π) ≈ 5 cm.

Front

What is the area of a circle with a diameter of 16 cm?

Back

A ≈ 200.96 cm².