A gymnasium inlays the floor with rectangular wood blocks of the same size, and paves two blocks for the first time, as shown in Figure 1. The second time completely encloses the first time, as shown in Figure 2 and figure 3 The second paving is completely enclosed, as shown in Figure 3. In this way, after the nth paving, the letter N is used to indicate the number of wood blocks used in the nth figure

A gymnasium inlays the floor with rectangular wood blocks of the same size, and paves two blocks for the first time, as shown in Figure 1. The second time completely encloses the first time, as shown in Figure 2 and figure 3 The second paving is completely enclosed, as shown in Figure 3. In this way, after the nth paving, the letter N is used to indicate the number of wood blocks used in the nth figure

Er Where is the picture?
Add 2 pieces for each girth, so
The nth graph [1 + 2 (n-1)] * [2 + 2 (n-1)] = (2n-1) * 2n = 4N & sup2; - 2n