If the diameter of a circle is 4 centimeters, what is its area in square centimetres? (π is calculated with 3.14)
一个圆的直径是4厘米，则它的面积是多少平方厘米．(π用3.14计算)
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

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

<gadget id="calculator">3.14 * 4</gadget>
<output>12.56</output>

<result>12.56</result>