Area and Circumference of Circles

Front

What is the definition of a circle?

Back

A circle is a shape consisting of all points in a plane that are a fixed distance (radius) from a central point (center).

Front

What is the radius of a circle?

Back

The radius is the distance from the center of the circle to any point on its circumference.

Front

What is the diameter of a circle?

Back

The diameter is the distance across the circle through the center, equal to twice the radius.

Front

What is the formula for the circumference of a circle?

Back

The circumference (C) is calculated using the formula: C = πd or C = 2πr, where d is the diameter and r is the radius.

Front

What is the formula for the area of a circle?

Back

The area (A) is calculated using the formula: A = πr², where r is the radius.

Front

If the radius of a circle is 7 inches, what is the area?

Back

A = π(7)² = 49π ≈ 153.94 in².

Front

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

Back

The radius is half of the diameter, so r = 10 cm / 2 = 5 cm.

Front

What is the circumference of a circle with a radius of 4 m?

Back

C = 2π(4) = 8π ≈ 25.13 m.

Front

How do you find the area of a circle if you know the diameter?

Back

First, find the radius by dividing the diameter by 2, then use the area formula A = πr².

Front

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

Back

C = π(12) ≈ 37.70 m.