The radius of the base of a cylinder is 4 cm, and when the sides are unfolded, it is exactly a square. What is the volume of the cylinder?
一个圆柱的底面半径为4厘米，侧面展开后正好是一个正方形，圆柱的体积是多少．
<gadget id="calculator">4 ** 2</gadget>
<output>16</output>

<gadget id="calculator">3.14 * 16</gadget>
<output>50.24</output>

<gadget id="calculator">2 * 3.14 * 4</gadget>
<output>25.12</output>

<gadget id="calculator">50.24 * 25.12</gadget>
<output>1_262.0288</output>

<result>1_262.0288</result>