| 2 | ÷ | ( | d | + | 2 | ) | + | 1 | ÷ | ( | d | + | 5 | ) | = | 0 |
| 方程两边同时乘以: | ( | d | + | 2 | ) |
| 2 | + | 1 | ÷ | ( | d | + | 5 | ) | × | ( | d | + | 2 | ) | = | 0 |
| 2 | + | 1 | ÷ | ( | d | + | 5 | ) | × | d | + | 1 | ÷ | ( | d | + | 5 | ) | × | 2 | = | 0 |
| 2 | + | 1 | ÷ | ( | d | + | 5 | ) | × | d | + | 2 | ÷ | ( | d | + | 5 | ) | = | 0 |
| 方程两边同时乘以: | ( | d | + | 5 | ) |
| 2 | ( | d | + | 5 | ) | + | 1 | d | + | 2 | = | 0 |
| 2 | d | + | 2 | × | 5 | + | 1 | d | + | 2 | = | 0 |
| 2 | d | + | 10 | + | 1 | d | + | 2 | = | 0 |
| 3 | d | + | 12 | = | 0 |
| 3 | d | = | 0 | − | 12 |
| 3 | d | = | - | 12 |
| d | = | - | 12 | ÷ | 3 |
| = | - | 12 | × | 1 3 |
| = | - | 4 | × | 1 |
| d | = | - | 4 |