| ( | 2 | d | + | 1 | ) | ( | d | + | 2 | ) | = | d | ( | d | + | 1 | ) |
| 方程左边 = | 2 | d | ( | d | + | 2 | ) | + | 1 | ( | d | + | 2 | ) |
| = | 2 | d | d | + | 2 | d | × | 2 | + | 1 | ( | d | + | 2 | ) |
| = | 2 | d | d | + | 4 | d | + | 1 | ( | d | + | 2 | ) |
| = | 2 | d | d | + | 4 | d | + | 1 | d | + | 1 | × | 2 |
| = | 2 | d | d | + | 4 | d | + | 1 | d | + | 2 |
| = | 2 | d | d | + | 5 | d | + | 2 |
| 2 | d | d | + | 5 | d | + | 2 | = | d | ( | d | + | 1 | ) |
| 方程右边 = | d | d | + | d | × | 1 |
| 2 | d | d | + | 5 | d | + | 2 | = | d | d | + | 1 | d |