If the lengths of the radii of two circles are 1 and 4 respectively, what is the ratio of their circumference and of their areas?

1 Answer
May 22, 2015

Circumference of a circle based on its radius
#C_r = 2pir#
The circumference of a circle is in direct proportion to the radius.
So two circles with radii in the ratio #1:4# will have circumferences in the ratio #1:4#

Area of a circle based on its radius
#A_r = pir^2#
The area of a circle is in direct proportion to the square of its radius.
So two circles with radii in the ration #1:4# will have areas in the ratio #1:16#