Circumference and Area of Circles

Front

What is the formula for the circumference of a circle?

Back

C = 2πr or C = πd, where r is the radius and d is the diameter.

Front

What is the formula for the area of a circle?

Back

A = πr², where r is the radius.

Front

If the radius of a circle is 7 cm, what is its circumference?

Back

C = 2π(7) ≈ 43.98 cm.

Front

If the diameter of a circle is 10 m, what is its area?

Back

A = π(5)² ≈ 78.54 m².

Front

What is the relationship between diameter and radius?

Back

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

Front

How do you convert diameter to radius?

Back

Divide the diameter by 2 (r = d/2).

Front

What is the circumference of a circle with a radius of 13.8 m?

Back

C = 2π(13.8) ≈ 86.66 m.

Front

What is the area of a circle with a radius of 7.5 m?

Back

A = π(7.5)² ≈ 176.71 m².

Front

What is the circumference of a circle with a diameter of 40 in?

Back

C = π(40) ≈ 125.6 in.

Front

If a circle has an area of 254.34 cm², what is its radius?

Back

r = √(A/π) ≈ 9 cm.