The lateral expansion of a cylinder is exactly a square. It is known that the radius of the base of the cylinder is 4cm. What is the height of the cylinder in cm?
一个圆柱的侧面展开恰好是一个正方形，已知圆柱的底面半径是4cm，这个圆柱的高是多少cm．
<gadget id="calculator">2 * 3.14 * 4</gadget>
<output>25.12</output>

<result>25.12</result>