cylinder with a base radius of 2 cm is a square when its sides are expanded. What is the area of its base?
一个圆柱底面半径2厘米，侧面展开后是一个正方形，它的底面面积是多少．
<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

<gadget id="calculator">3.14 * 4</gadget>
<output>12.56</output>

<result>12.56</result>