The radius of the base of a cylinder is 4 cm, and its sides are expanded to form a square. What is the side length of this square in cm?
一个圆柱体的底面半径是4厘米，它的侧面展开得到一个正方形，这个正方形的边长是多少厘米．
<gadget id="calculator">2 * 3.14 * 4</gadget>
<output>25.12</output>

<result>25.12</result>