The radius of the base of a cylinder is 2 cm, and the sides are unfolded to form a square. What is the height of the cylinder?
一个圆柱的底面半径为2厘米，侧面展开后正好是一个正方形，圆柱的高是多少．
<gadget id="calculator">3.14 * 2 * 2</gadget>
<output>12.56</output>

<result>12.56</result>