If the radius of the small circle is (1/2) of the radius of the large circle, then the area of the small circle is equal to the area of the large circle.
小圆半径是大圆半径的(1/2)，则小圆面积是大圆面积的多少．
<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<result>1/4 = around 0.25</result>