If the central angle of the fan is 45°, the area of the fan is the area of the circle where it is located
扇形的圆心角是45°，则扇形的面积是所在圆面积的多少
<gadget id="calculator">45 / 360</gadget>
<output>1/8 = around 0.125</output>

<result>1/8 = around 0.125</result>