Area 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

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

Back

The radius is 5 cm, since the radius is half of the diameter.

Front

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

Back

A = π(4)² = 16π in².

Front

How do you find the area of a semicircle?

Back

Area of semicircle = (1/2)πr².

Front

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

Back

A = π(6)² = 36π cm².

Front

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

Back

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

Front

What is the area of a circle with a radius of 3 feet?

Back

A = π(3)² = 9π ft².

Front

What shape is formed when a circle is folded in half?

Back

A semicircle.

Front

What is the approximate area of a circle with a radius of 7 inches?

Back

A ≈ 49π in² or approximately 153.94 in².

Front

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

Back

A = π(10)² = 100π cm².