As shown in the figure, the side length of square ABCD is equal to 2 1, which is divided into four rectangles: CPFN, BMFP, AQEM and DNEQ ... The area ratio of these four rectangles is.
Bp = 21× 21+2 =14 (cm)
AQ=2 1×33+4=9 (cm)
EF= 14-9=5 (cm)
Area of shaded part:
5×5=25 (square centimeter)
The area of this square is 25 square centimeters.
So the answer is: 25 square centimeters.