If the radius of a circle increases from 2 cm to 3 cm, its area increases by π square centimeters.
一个圆的半径由2厘米增加到3厘米，它的面积增加了多少π平方厘米．
<gadget id="calculator">3 ** 2</gadget>
<output>9</output>

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

<gadget id="calculator">9 - 4</gadget>
<output>5</output>

<result>5</result>