it depends no of variables in the figure in circle only one variable is there radius , in square one variable is there side
so in above case u can have relationship b/w perimeter and area
Even otherwise u have a relationship. Thats why I said REGULAR.. n-sided polygon.
Is its regular then u can get the side == perimeter/n (where n is the no of sides)
and then you can get the value of each angle! Which is equal to (2n -4)*90/n degrees! This is because the sum of the interior angles of a polygon is (2n-1)*90 degrees. Since its regular its divide by the number of sides!
Now since u have the length of the side and the measure of each angle, you can use trignometry to find the rest! (Essentially u can break the regular polugons into n triangles, use trig to compute the area of each and then multiple it by n!!)