math

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

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asked by Thomas
  1. 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

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    posted by Damon

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