| 4 | ( | 9 | x | − | 17 | ) | − | 9 | ( | x | + | 12 | ) | − | 1 | = | 12 |
| 方程左边 = | 4 | × | 9 | x | − | 4 | × | 17 | − | 9 | ( | x | + | 12 | ) | − | 1 |
| = | 36 | x | − | 68 | − | 9 | ( | x | + | 12 | ) | − | 1 |
| = | 36 | x | − | 69 | − | 9 | ( | x | + | 12 | ) |
| = | 36 | x | − | 69 | − | 9 | x | − | 9 | × | 12 |
| = | 36 | x | − | 69 | − | 9 | x | − | 108 |
| = | 27 | x | − | 177 |
| 27 | x | − | 177 | = | 12 |
| 27 | x | = | 12 | + | 177 |
| 27 | x | = | 189 |
| x | = | 189 | ÷ | 27 |
| = | 189 | × | 1 27 |
| = | 7 | × | 1 |
| x | = | 7 |