7.9B Circumference and Area of Circles

Front

What is the diameter of a circle?

Back

The distance from an edge of a circle to another edge through the center.

Front

How do you find the area of a circle?

Back

Area = π × radius². For example, if the radius is 7 cm, Area = π × (7)² = 153.86 cm².

Front

What is the formula for the circumference of a circle?

Back

Circumference = 2 × π × radius. For example, for a radius of 13.5 mm, Circumference = 2 × π × 13.5 ≈ 84.78 mm.

Front

What is the radius of a circle?

Back

The measurement from the center of a circle to an edge of the circle.

Front

What is the area of a circle with a diameter of 18 cm?

Back

Area = π × (radius)² = π × (9)² ≈ 254.34 cm².

Front

What does π (pi) represent in circle calculations?

Back

π (pi) is a constant approximately equal to 3.14, used in calculations involving circles.

Front

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

Back

The area increases by a factor of four, since Area = π × (2 × radius)² = 4 × (π × radius²).

Front

What is the relationship between diameter and radius?

Back

The diameter is twice the radius. Diameter = 2 × radius.

Front

How do you convert diameter to radius?

Back

Radius = Diameter ÷ 2.

Front

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

Back

Circumference = 2 × π × 5 ≈ 31.42 cm.