In a circle, make a square with its radius as the side length. The area of the square is 25 square centimeters. What is the area of the circle in square centimeters?
在一个圆内，以它的半径为边长做一个正方形，已知正方形的面积是25平方厘米，圆的面积是多少平方厘米．
<gadget id="calculator">3.14 * 25</gadget>
<output>78.5</output>

<result>78.5</result>