Cut a square iron sheet with a side length of 10dm into the largest round iron cover, what is the area of this round iron cover in dm**2.
把一个边长为10dm的正方形铁皮，剪成一个最大的圆铁盖，这个圆铁盖的面积为多少dm**2．
<gadget id="calculator">10 / 2</gadget>
<output>5</output>

<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

<gadget id="calculator">3.14 * 25</gadget>
<output>78.5</output>

<result>78.5</result>