| ( | 18 | ÷ | x | ) | − | ( | 21 | ÷ | x | + | 30 | ) | = | 1 |
| 18 | ÷ | x | − | ( | 21 | ÷ | x | + | 30 | ) | = | 1 |
| 方程两边同时乘以: | x |
| 18 | − | ( | 21 | ÷ | x | + | 30 | ) | x | = | 1 | x |
| 18 | − | 21 | ÷ | x | × | x | − | 30 | x | = | 1 | x |
| - | 30 | x | − | 1 | x | = | - | 18 | + | 21 | ÷ | 1 | × | 1 |
| - | 30 | x | − | 1 | x | = | - | 18 | + | 21 |
| - | 31 | x | = | - | 18 | + | 21 |
| - | 31 | x | = | 3 |
| - | 3 | = | 31 | x |
| 31 | x | = | - | 3 |
| x | = | - | 3 | ÷ | 31 |
| = | - | 3 | × | 1 31 |
| x | = | - | 3 31 |
| x | = | - 0.096774 |