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 5 cm, what is its area?

Back

A = π(5)² ≈ 78.54 cm².

Front

What is the value of π (pi) approximately?

Back

π ≈ 3.14.

Front

How do you find the diameter of a circle 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 circumference of 31.4 cm, what is its radius?

Back

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

Front

What is the area of a circle with a diameter of 10 cm?

Back

Radius (r) = 10/2 = 5 cm; A = π(5)² ≈ 78.54 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.