If the central angle of a fan is doubled and the radius is reduced to half, what is the area of the fan?
把一个扇形的圆心角扩大到原来2倍，半径缩小到原来的一半，则其面积变为原来的多少
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<result>1/2 = around 0.5</result>