7.9B Circumference and Area of Circles

Front

What is the formula for the circumference of a circle?

Back

Circumference = π × diameter or Circumference = 2 × π × radius.

Front

What is the value of π (pi) approximately?

Back

π (pi) is approximately 3.14.

Front

If a circle has a diameter of 10 cm, what is its circumference?

Back

Circumference = π × diameter = 3.14 × 10 = 31.4 cm.

Front

What is the relationship between diameter and radius?

Back

The radius is half of the diameter. Radius = diameter / 2.

Front

How do you find the area of a circle?

Back

Area = π × radius².

Front

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

Back

Area = π × (5)² = π × 25 ≈ 78.5 cm².

Front

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

Back

Circumference = 2 × π × 7 ≈ 43.96 m.

Front

If the circumference of a circle is 62.8 cm, what is its diameter?

Back

Diameter = Circumference / π = 62.8 / 3.14 ≈ 20 cm.

Front

What is the diameter of a circle with a circumference of 31.4 m?

Back

Diameter = Circumference / π = 31.4 / 3.14 = 10 m.

Front

How do you convert diameter to radius?

Back

Divide the diameter by 2.