A = pi r^2
A' = 9 pi (r)^2 = pi R^2
so R^2/r^2 = 9
R/r = 3
circumference proportional to radius
so
THREE times
If the area of a circle is increased by a factor of 9, the circumference of that circle will be increased by what factor?
a. 3
b. 6
c. 9
d. 18
e. 81
please answer and explain
1 answer