Circles - Area and Circumference

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 diameter of 10 cm, what is its radius?

Back

The radius is 5 cm.

Front

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

Back

C = 2π(7) = 43.96 inches.

Front

If the area of a circle is 78.5 square meters, what is the radius?

Back

r = √(A/π) = √(78.5/π) ≈ 5 meters.

Front

What is the value of π (pi) approximately?

Back

π ≈ 3.14.

Front

How do you calculate the diameter of a circle if you know the radius?

Back

Diameter (d) = 2 × radius (r).

Front

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

Back

C = πd = π(12) ≈ 37.68 cm.

Front

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

Back

The area increases by a factor of 4.

Front

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

Back

A = π(3)² = 28.26 square cm.