| ( | X | − | 50 | ) | ( | - | 10 | X | + | 1100 | ) | = | 8000 |
| 方程左边 = | X | ( | - | 10 | X | + | 1100 | ) | − | 50 | ( | - | 10 | X | + | 1100 | ) |
| = | - | X | × | 10 | X | + | X | × | 1100 | − | 50 | ( | - | 10 | X | + | 1100 | ) |
| = | - | X | × | 10 | X | + | 1100 | X | + | 50 | × | 10 | X | − | 50 | × | 1100 |
| = | - | X | × | 10 | X | + | 1100 | X | + | 500 | X | − | 55000 |
| = | - | X | × | 10 | X | + | 1600 | X | − | 55000 |
| - | X | × | 10 | X | + | 1600 | X | − | 55000 | = | 8000 |