Area and Circumference 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 5 inches, what is the circumference?

Back

31.4 inches (C = 2π(5) ≈ 31.4).

Front

What is the relationship between diameter and radius?

Back

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

Front

What is the diameter of a circle with a radius of 4 inches?

Back

8 inches (d = 2r = 2(4)).

Front

What is the distance halfway across a circle called?

Back

Radius.

Front

If a circle has a diameter of 10 inches, what is its radius?

Back

5 inches (r = d/2 = 10/2).

Front

What is the area of a circle with a radius of 4 inches?

Back

16π square inches (A = π(4)² = 16π).

Front

How do you convert the area of a circle from square units to a numerical approximation?

Back

Multiply the area in terms of π by the approximate value of π (≈ 3.14).

Front

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

Back

21.98 inches (C = πd = π(7) ≈ 21.98).