The area A of a circle is directly proportional to the square of its radius. The area of a circle with a diameter of 40 cm is 1 256 sq. cm.

Question

Continuation... What is the area of a circle with a diameter of a) 20 cm? b) 10 cm c) 12 cm? d) 30?

a) A =

b) A=

c) A =

d) A =

Answer 1

a) area = about 3.14(10)^2 = 3.14(100) = 314 cm^2

b) area = about 3.14(5)^2 = 3.14(25) = 78.5 cm^2

c) area = about 3.14(6)^2 = 3.14(36) = 113 cm^2

d) area = about 3.14(15^2) = 3.14(225) = 706.5 cm^2

area = pi(r^2) = pi(d/2)^2 = about 3.14(d^2)/4