If the central angle of the fan is doubled and the radius is reduced to 1/2, the area of the fan is reduced to the original
扇形的圆心角扩大为原来的2倍，半径缩小为原来的(1/2)，则扇形的面积缩小为原来的多少
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

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