A cylinder with a base radius of 5 cm is exactly a square when its sides are expanded. What is its height?
一个底面半径是5厘米的圆柱侧面展开后正好是一个正方形，它的高是多少．
<gadget id="calculator">2 * 3.14 * 5</gadget>
<output>31.4</output>

<result>31.4</result>