It is known that the diameter of the bottom surface of the cylinder is 4cm, and its side along the height is exactly a square, then what is the height of the cylinder in cm?
已知圆柱的底面直径是4cm，把它的侧面沿高展开正好是一个正方形，那么这个圆柱的高是多少cm．
<gadget id="calculator">3.14 * 4</gadget>
<output>12.56</output>

<result>12.56</result>