CIrcumference & Area of Circles

Front

What is the formula for the area of a circle?

Back

A = π × r × r, where A is the area and r is the radius.

Front

What is the formula for the circumference of a circle?

Back

C = 2 × π × r, where C is the circumference and r is the radius.

Front

If the diameter of a circle is 16 cm, what is the radius?

Back

The radius is 8 cm, since the radius is half of the diameter.

Front

What is the area of a circle with a radius of 12 cm?

Back

A = π × 12 × 12 ≈ 452.39 cm².

Front

How do you convert diameter to radius?

Back

Divide the diameter by 2.

Front

What is the circumference of a circle with a radius of 10 cm?

Back

C = 2 × π × 10 ≈ 62.83 cm.

Front

What is the area of a circle with a diameter of 20 cm?

Back

First, find the radius (10 cm), then A = π × 10 × 10 ≈ 314.16 cm².

Front

If the area of a circle is 254.34 cm², what is the radius?

Back

r = √(A/π) ≈ √(254.34/π) ≈ 9 cm.

Front

What is the relationship between diameter and circumference?

Back

The circumference is π times the diameter (C = π × d).

Front

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

Back

First, find the radius using r = C/(2π), then use A = π × r × r.