d | ( | 2 | d | + | 3 | ) | + | ( | d | + | 1 | ) | ( | d | + | 2 | ) | = | 0 |
方程左边 = | d | × | 2 | d | + | d | × | 3 | + | ( | d | + | 1 | ) | ( | d | + | 2 | ) |
= | d | × | 2 | d | + | 3 | d | + | d | ( | d | + | 2 | ) | + | 1 | ( | d | + | 2 | ) |
= | d | × | 2 | d | + | 3 | d | + | d | d | + | d | × | 2 | + | 1 | ( | d | + | 2 | ) |
= | d | × | 2 | d | + | 5 | d | + | d | d | + | 1 | ( | d | + | 2 | ) |
= | d | × | 2 | d | + | 5 | d | + | d | d | + | 1 | d | + | 1 | × | 2 |
= | d | × | 2 | d | + | 5 | d | + | d | d | + | 1 | d | + | 2 |
= | d | × | 2 | d | + | 6 | d | + | d | d | + | 2 |
d | × | 2 | d | + | 6 | d | + | d | d | + | 2 | = | 0 |