Cut a small square of four centimeters from each corner of the square iron sheet to make a box without a lid. It is known that the volume of this box is 400 cubic centimeters. ...
Solution: The side length of square iron sheet should be x cm. According to the equation, (x-4×2)(x-4×2)×4=400.
The solution is x 1= 18, x2=-2 (irrelevant, omitted);
Answer: The side length of the square iron sheet should be 18 cm.