The radius of the base of a cylinder is 2 cm, and a square is obtained after unfolding the sides, then what is the side area of the cylinder in square centimeters?
一个圆柱底面半径是2厘米，将侧面展开后得到一个正方形，那么这个圆柱的侧面积是多少平方厘米．
<gadget id="calculator">3.14 * 2 * 2</gadget>
<output>12.56</output>

<gadget id="calculator">12.56 * 12.56</gadget>
<output>157.7536</output>

<result>157.7536</result>