Divide a circle into 1000 perfectly equal small sectors on average, and then put together an approximate rectangle whose circumference is 10 cm longer than that of the circle. What is the area of this circle in square centimetres.
把一个圆平均分成1000个完全相等的小扇形，然后拼成一个近似的长方形的周长比圆的周长多10厘米．这个圆的面积是多少平方厘米．
<gadget id="calculator">10 / 2</gadget>
<output>5</output>

<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

<gadget id="calculator">3.14 * 25</gadget>
<output>78.5</output>

<result>78.5</result>