



 
Hi Niki.
The best way to approach this is to center the circle on the origin of a normal graph and use x as your independent variable. Now it should be clear to you that the perimeter is simply 4(x+y). Thus, we really only need to think about the first quadrant. x varies from 0 to R, of course, and so does y. But you can express f(x) = y by rearranging the circle's equation R^{2} = x^{2} + y^{2}. Then just find the minimum and maximum values of the expression x + f(x) and multiply by four. Write back if you need more hints.
Cheers,  


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