Solution: the side length of a square is x, and the area of a square is x?

AD = 40 x EC = 60 x

△ area of △ADF = (40-x) x△ area of cef =(60-x)x

∴x？ = 40×60÷2-[(40-x)x]÷2-[(60-x)x]÷2

2x？ =2400-40x+x？ -60x+x？

x=24

x？ =576

The area of a square is 576 square centimeters.