| ( | - | 8 | x | + | 136 | ) | ( | x | − | 9 | ) | = | 128 |
| 方程左边 = | - | 8 | x | ( | x | − | 9 | ) | + | 136 | ( | x | − | 9 | ) |
| = | - | 8 | x | x | + | 8 | x | × | 9 | + | 136 | ( | x | − | 9 | ) |
| = | - | 8 | x | x | + | 72 | x | + | 136 | ( | x | − | 9 | ) |
| = | - | 8 | x | x | + | 72 | x | + | 136 | x | − | 136 | × | 9 |
| = | - | 8 | x | x | + | 72 | x | + | 136 | x | − | 1224 |
| = | - | 8 | x | x | + | 208 | x | − | 1224 |
| - | 8 | x | x | + | 208 | x | − | 1224 | = | 128 |