The radius of the circle increases from 2cm to 3cm, how much does the area of the circle increase by πcm**2.
圆的半径由2cm，增加到3cm，这个圆的面积增加了多少πcm**2．
<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

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

<result>5</result>