What do you mean by equivalent? Because your answer for a circle is the value of pi (3.14159), the only sensible meaning is perimeter. For a circle this is 2(pi)r where r is the radius, here equal to 1/2 for the result 2(pi)(1/2) = pi. Now we could say that a (square having pi/4 side length) will also have a value of pi for its perimeter since how r transfers from the circle to the square isn't specified. It also could be interpreted that r = 1/2 is the distance from the center to a side of the square if a perpendicular is drawn which would mean each side is 1 and four of them is four. Finally r = 1/2 could be the distance from the center to a corner of the square, making each side equal sqrt[1/2] and the perimeter equal to 4 of hem. Be careful to ask for what you want if you expect a clear answer.