Area & Circumference of Circles

Front

What is the formula for the area of a circle?

Back

A = πr², where A is the area and r is the radius.

Front

What is the formula for the circumference of a circle?

Back

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

Front

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

Back

The area increases by a factor of four.

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 10 inches?

Back

C = 2π(10) = 20π ≈ 62.83 inches.

Front

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

Back

A = π(5)² = 25π ≈ 78.54 ft².

Front

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

Back

C = π(12) ≈ 37.70 cm.

Front

If a cow is tied with a rope of length 20 ft, what is the area in which it can graze?

Back

Area = π(20)² = 400π ≈ 1256.64 ft².

Front

What is the diameter of a circle with a radius of 4 inches?

Back

Diameter = 2 * 4 = 8 inches.