If the radius of a circle increases from 2cm to 5cm, the area of the circle increases by cm**2.
一个圆的半径由2cm增加到5cm，这个圆的面积就增加多少cm**2．
<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

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

<gadget id="calculator">25 - 4</gadget>
<output>21</output>

<gadget id="calculator">3.14 * 21</gadget>
<output>65.94</output>

<result>65.94</result>