| ( | 101 | x | − | 7100 | ) | ( | - | 10 | x | + | 700 | ) | = | 7900 |
| 方程左边 = | 101 | x | ( | - | 10 | x | + | 700 | ) | − | 7100 | ( | - | 10 | x | + | 700 | ) |
| = | - | 101 | x | × | 10 | x | + | 101 | x | × | 700 | − | 7100 | ( | - | 10 | x | + | 700 | ) |
| = | - | 1010 | x | x | + | 70700 | x | − | 7100 | ( | - | 10 | x | + | 700 | ) |
| = | - | 1010 | x | x | + | 70700 | x | + | 7100 | × | 10 | x | − | 7100 | × | 700 |
| = | - | 1010 | x | x | + | 70700 | x | + | 71000 | x | − | 4970000 |
| = | - | 1010 | x | x | + | 141700 | x | − | 4970000 |
| - | 1010 | x | x | + | 141700 | x | − | 4970000 | = | 7900 |