Prove: As shown in Figure 3. Let the areas of the triangular flaps as R and S respectively, and the area of triangle AEG as T. Then the area of the whole square is 2R + 2S + T. Assuming that the length of one side of the square is 1 and letting BG = x, then R = 1/4, S = x/2, T = 1 − x/4. Therefore, the expression of the square area will be 1/2+x+1−x/4=1. From this equation, we obtain x = 1/3.