Expert: Bobby Soltani - 4/22/2005

Question
If the radius of a circle is trippled, what would happen to the area? please explain

Answer
Hi Tamara,

I'll try to explain.

The area of a circle is A = pi*r^2
Let's call the original circle C1, then the area was A1 = pi*(r1)^2, where A1 is the area of the first circle and r1 is the radius of the first circle.  The equation for the area of the second circle(with a radius that is triple the first) is A2 = pi*(3*r1)^2, which is equal to A2 = 9*pi*r1^2.  If we look at this equation, we can see that pi*r1^2 is the equation for A1, so we can substitute it in and write:

A2 = 9*A1

So, the are increased by a factor of 9.

Let me know if you have any questions.

Bobby