When we were exploring the formula for calculating the area of a circle, we cut a circular piece of paper along the radius to form an approximate rectangle. As a result, Xiao Ming found that the perimeter of the rectangle was 4cm longer than the perimeter of the circle. Then the area of the circle should be How many square centimeters is it.
我们在探索圆的面积计算公式时，把一个圆纸片沿半径剪拼成了一个近似的长方形后，结果小明发现这个长方形的周长比圆的周长多了4cm，那么这个圆的面积应是多少平方厘米．
<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>