If the radius of a circle increases from 5 cm to 8 cm, the area of the circle increases by П square centimeters.
一个圆的半径由5厘米增加到8厘米，圆的面积增加多少П平方厘米．
<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

<gadget id="calculator">64 - 25</gadget>
<output>39</output>

<result>39</result>