Expand the sides of a cylinder to get a square. The radius of the base of the cylinder is 4 decimeters. What is its height in decimeters?
把一个圆柱的侧面展开，得到一个正方形，圆柱的底面半径是4分米，它的高是多少分米．
<gadget id="calculator">3.14 * 4 * 2</gadget>
<output>25.12</output>

<result>25.12</result>