| 15 | x | = | ( | x | − | 6 | ) | ( | 15 | + | 3 | ) |
| 方程右边 = | x | ( | 15 | + | 3 | ) | − | 6 | ( | 15 | + | 3 | ) |
| = | x | × | 15 | + | x | × | 3 | − | 6 | ( | 15 | + | 3 | ) |
| = | 18 | x | − | 6 | ( | 15 | + | 3 | ) |
| = | 18 | x | − | 6 | × | 15 | − | 6 | × | 3 |
| = | 18 | x | − | 90 | − | 18 |
| = | 18 | x | − | 108 |
| 15 | x | = | 18 | x | − | 108 |
| 15 | x | − | 18 | x | = | - | 108 |
| - | 3 | x | = | - | 108 |
| 108 | = | 3 | x |
| 3 | x | = | 108 |
| x | = | 108 | ÷ | 3 |
| = | 108 | × | 1 3 |
| = | 36 | × | 1 |
| x | = | 36 |