Area and circumference

Front

What is the formula for the circumference of a circle?

Back

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

Front

What is the formula for the area of a circle?

Back

A = πr², where r is the radius.

Front

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

Back

The radius is 5 cm.

Front

What is the circumference of a circle with a radius of 12.5 mm?

Back

78.5 mm.

Front

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

Back

A = π(5)² = 25π or about 78.54 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 20 cm?

Back

C = π(20) = 20π or about 62.83 cm.

Front

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

Back

The area increases by a factor of 4.

Front

What is the relationship between diameter and circumference?

Back

Circumference is π times the diameter.

Front

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

Back

A = π(10)² = 100π or about 314.16 cm².