CIrcumference & 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 area?

Back

A = π(7)² = 49π ≈ 153.86 cm².

Front

If the diameter of a circle is 14 cm, what is its circumference?

Back

C = πD = π(14) ≈ 43.98 cm.

Front

What is the value of π (pi) approximately?

Back

π ≈ 3.14.

Front

How do you convert diameter to radius?

Back

Radius (r) = Diameter (D) / 2.

Front

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

Back

C = 2π(10) = 20π ≈ 62.83 cm.

Front

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

Back

A = π(5)² = 25π ≈ 78.54 cm².

Front

If a circle has an area of 100π cm², what is its radius?

Back

r = √(A/π) = √(100) = 10 cm.

Front

What happens to the area of a circle if the radius is doubled?

Back

The area increases by a factor of 4 (A = π(2r)² = 4πr²).