| 1 | ÷ | ( | d | + | 1 | ) | + | 1 | ÷ | ( | d | + | 4 | ) | = | 0 |
| 方程两边同时乘以: | ( | d | + | 1 | ) |
| 1 | + | 1 | ÷ | ( | d | + | 4 | ) | × | ( | d | + | 1 | ) | = | 0 |
| 1 | + | 1 | ÷ | ( | d | + | 4 | ) | × | d | + | 1 | ÷ | ( | d | + | 4 | ) | × | 1 | = | 0 |
| 1 | + | 1 | ÷ | ( | d | + | 4 | ) | × | d | + | 1 | ÷ | ( | d | + | 4 | ) | = | 0 |
| 方程两边同时乘以: | ( | d | + | 4 | ) |
| 1 | ( | d | + | 4 | ) | + | 1 | d | + | 1 | = | 0 |
| 1 | d | + | 1 | × | 4 | + | 1 | d | + | 1 | = | 0 |
| 1 | d | + | 4 | + | 1 | d | + | 1 | = | 0 |
| 2 | d | + | 5 | = | 0 |
| 2 | d | = | 0 | − | 5 |
| 2 | d | = | - | 5 |
| d | = | - | 5 | ÷ | 2 |
| = | - | 5 | × | 1 2 |
| d | = | - | 5 2 |
| d | = | - 2.5 |