Circles: Area & Circumference

Front

What is the formula for the area of a circle?

Back

Area = πr², where r is the radius.

Front

What is the formula for the circumference of a circle?

Back

Circumference = 2πr or Circumference = πd, where d is the diameter.

Front

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

Back

154 cm² (Area = π(7)² = 49π).

Front

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

Back

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

Front

What is the diameter of a circle if the radius is 10 cm?

Back

20 cm (Diameter = 2r).

Front

How do you convert diameter to radius?

Back

Radius = Diameter / 2.

Front

What is the area of a circle with a diameter of 12 m?

Back

113.04 m² (Area = π(6)² = 36π).

Front

If the area of a circle is 78.54 cm², what is the radius?

Back

5 cm (Area = πr², so r = √(78.54/π)).

Front

What is the relationship between radius and diameter?

Back

The diameter is twice the radius.

Front

How do you find the area of a circle if you only know the circumference?

Back

First, find the radius using r = Circumference / (2π), then use Area = πr².