The lateral expansion of a cylinder is a square. It is known that the radius of the base of the cylinder is 5 cm. What is the height of the cylinder?
一个圆柱的侧面展开是正方形，已知圆柱底面半径是5厘米，圆柱的高是多少．
<gadget id="calculator">3.14 * 2 * 5</gadget>
<output>31.4</output>

<result>31.4</result>