| 1 | ÷ | d | + | 7 | = | 1 | ÷ | d | + | 1 | ÷ | d | + | 3 | + | 1 | ÷ | d | + | 7 |
| 方程两边同时乘以: | d |
| 1 | + | 7 | d | = | 1 | ÷ | 1 | × | 1 | + | 1 | ÷ | 1 | × | 1 | + | 3 | d | + | 1 | ÷ | 1 | × | 1 | + | 7 |
| 7 | d | − | 3 | d | − | 7 | d | = | 1 | ÷ | 1 | × | 1 | + | 1 | ÷ | 1 | × | 1 | + | 1 | ÷ | 1 | × | 1 | − | 1 |
| 7 | d | − | 3 | d | − | 7 | d | = | 1 | + | 1 | + | 1 | − | 1 |
| - | 3 | d | = | 1 | + | 1 | + | 1 | − | 1 |
| - | 3 | d | = | 2 |
| - | 2 | = | 3 | d |
| 3 | d | = | - | 2 |
| d | = | - | 2 | ÷ | 3 |
| = | - | 2 | × | 1 3 |
| d | = | - | 2 3 |
| d | = | - 0.666667 |