Expand the side of a cylinder to get a square. The radius of this cylinder is 5 cm. What is its height in cm?
把一个圆柱的侧面展开，得到一个正方形，这个圆柱的半径是5cm，它的高是多少cm．
<gadget id="calculator">2 * 3.14 * 5</gadget>
<output>31.4</output>

<result>31.4</result>