circumference and Area of a Circle

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 value of π (pi) approximately?

Back

π is approximately 3.14.

Front

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

Back

C = 2π(7) = 14π ≈ 43.98 cm.

Front

What is the formula for the area of a circle?

Back

A = πr², where r is the radius.

Front

If the diameter of a circle is 10 cm, what is the radius?

Back

The radius is half of the diameter, so r = 10 cm ÷ 2 = 5 cm.

Front

What is the area of a circle with a radius of 4 cm?

Back

A = π(4)² = 16π ≈ 50.27 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 diameter of 12 cm?

Back

C = πd = π(12) = 12π ≈ 37.68 cm.

Front

If a circle has a circumference of 31.4 cm, what is its radius?

Back

C = 2πr, so r = C/(2π) = 31.4/(2π) ≈ 5 cm.

Front

What is the relationship between radius and diameter?

Back

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