Cut a circle into an approximate rectangle whose width is equal to the radius of the circle and whose area remains the same. It is known that the perimeter of this rectangle is 16.56 cm. How big is the cut circle?
把一个圆形剪拼成一个近似长方形，这个长方形的宽等于圆的半径，面积不变．已知这个长方形周长是16.56厘米．剪开的圆形有多大？
<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

<gadget id="calculator">3.14 * 4</gadget>
<output>12.56</output>

<result>12.56</result>