A cylinder is formed by a square iron sheet whose side length is 40 cm. What is the lateral area of the cylinder?
用一张边长是40厘米的正方形铁皮，围成一个圆柱体，这个圆柱体的侧面积是多少．
<gadget id="calculator">40 * 40</gadget>
<output>1_600</output>

<result>1_600</result>