Area and Circumference of Circles

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

What is the formula for the circumference of a circle?

Back

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

Front

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

Back

A = π(10)² = 100π cm².

Front

If the diameter of a circle is 20 cm, what is its circumference?

Back

C = π(20) = 20π cm.

Front

What does 'r' represent in the formulas for area and circumference of a circle?

Back

'r' represents the radius of the circle.

Front

What does 'd' represent in the formula C = π·d?

Back

'd' represents the diameter of the circle.

Front

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

Back

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

Front

What is the area of a circle with a radius of 5 cm?

Back

A = π(5)² = 25π cm².

Front

What is the circumference of a circle with a radius of 7 cm?

Back

C = 2π(7) = 14π cm.

Front

If a circle has an area of 36π ft², what is its radius?

Back

r = √(36) = 6 ft.