| ( | 61 100 | − | x | ) | ( | 1 10 | − | x | ) | = | 21 100 | × | 21 100 |
| 方程左边 = | 61 100 | ( | 1 10 | − | x | ) | − | x | ( | 1 10 | − | x | ) |
| = | 61 100 | × | 1 10 | − | 61 100 | x | − | x | ( | 1 10 | − | x | ) |
| = | 61 1000 | − | 61 100 | x | − | x | ( | 1 10 | − | x | ) |
| = | 61 1000 | − | 61 100 | x | − | x | × | 1 10 | + | x | x |
| = | 61 1000 | − | 71 100 | x | + | x | x |
61 1000 | − | 71 100 | x | + | x | x | = | 21 100 | × | 21 100 |
| 方程右边 = | 441 10000 |
61 1000 | − | 71 100 | x | + | x | x | = | 441 10000 |