| 7 | ( | - | x | + | 1 | ) | + | 5 | ( | x | − | 9 | ) | + | 5 | = | - | 9 |
| 方程左边 = | - | 7 | x | + | 7 | × | 1 | + | 5 | ( | x | − | 9 | ) | + | 5 |
| = | - | 7 | x | + | 7 | + | 5 | ( | x | − | 9 | ) | + | 5 |
| = | - | 7 | x | + | 12 | + | 5 | ( | x | − | 9 | ) |
| = | - | 7 | x | + | 12 | + | 5 | x | − | 5 | × | 9 |
| = | - | 7 | x | + | 12 | + | 5 | x | − | 45 |
| = | - | 2 | x | − | 33 |
| - | 2 | x | − | 33 | = | - | 9 |
| - | 2 | x | = | - | 9 | + | 33 |
| - | 2 | x | = | 24 |
| - | 24 | = | 2 | x |
| 2 | x | = | - | 24 |
| x | = | - | 24 | ÷ | 2 |
| = | - | 24 | × | 1 2 |
| = | - | 12 | × | 1 |
| x | = | - | 12 |