Expert: Ahmed Salami - 6/8/2004

Question
If I have a circle with a radius of one inch. To draw a circle with an area four times as large. What is the change in the radius?

Answer
Hi
Sorry its a bit late.
We know that the area of a circle of radius r is #r^2.
If we decide to work in inches,then the area of the first circle is #(1^2) = #
If the new circle is to have a radius k, then
4# = #k^2
which gives us
k = 2
So there is only a change of an inch in the radius.
Generally,
(A1)/(A2) = (r1)^2/(r2)^2
if we were to use this, then
4 = k^2
k = 2
as before.

Hope it was helpful.
You can always ask more.