Circumference and Area of Circles

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 7 cm, what is its circumference?

Back

C = 2π(7) ≈ 43.98 cm.

Front

If the radius of a circle is 10 cm, what is its area?

Back

A = π(10)² ≈ 314.16 cm².

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 of a circle to its diameter.

Front

How do you convert diameter to radius?

Back

Radius (r) = Diameter (d) / 2.

Front

What is the relationship between diameter and circumference?

Back

Circumference (C) = π × Diameter (d).

Front

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

Back

r = C / (2π) = 31.4 / (2π) ≈ 5 cm.

Front

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

Back

A = π(6)² ≈ 113.10 cm².

Front

How does increasing the radius affect the area of a circle?

Back

The area increases with the square of the radius; doubling the radius increases the area by a factor of four.