The radius of the outer circle of a circular washer is 2 cm and the radius of the inner circle is 1 cm. What is the area of the washer in square centimeters?
一个环形垫圈的外圆半径是2厘米，内圆半径是1厘米，这个垫圈的面积是多少平方厘米．
<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

<gadget id="calculator">1 ** 2</gadget>
<output>1</output>

<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">3.14 * 3</gadget>
<output>9.42</output>

<result>9.42</result>