The outer diameter of a circular tank is 1 meter. Make a cover for this tank. What is the minimum area of the cover?
一个圆形水缸的外直径为1米，为这个水缸做一个盖子，这个盖子的面积至少是多少？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) ** 2</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">3.14 * (1/4)</gadget>
<output>0.785</output>

<result>0.785</result>