A circle is surrounded by an iron wire, and its diameter is exactly 10dm. If this iron wire is used to form a square, what is the side length of the square in dm?
用一根铁丝围成一个圆，直径正好是10dm，如果用这根铁丝围成一个正方形，正方形的边长是多少dm．
<gadget id="calculator">3.14 / 4</gadget>
<output>0.785</output>

<gadget id="calculator">10 * 0.785</gadget>
<output>7.85</output>

<result>7.85</result>