What is the area of a sector of arc length 5 cm in a circle of diameter 4 cm?
直径为4cm的圆中，弧长为5cm的扇形的面积是多少．
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

<gadget id="calculator">3.14 * 4</gadget>
<output>12.56</output>

<gadget id="calculator">5 / 12.56</gadget>
<output>0.398089</output>

<gadget id="calculator">12.56 * 0.398089</gadget>
<output>4.999998</output>

<result>4.999998</result>