The silver part of the CD is a ring, the radius of the inner circle is 2cm, and the radius of the outer circle is 3cm. What is the area of the ring?
光盘的银色部分是一个圆环，内圆半径是2cm，外圆半径是3cm，圆环面积是多少．
<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>

<gadget id="calculator">3.14 * 5</gadget>
<output>15.7</output>

<result>15.7</result>