| 100 | × | 90 100 | x | = | 10 | × | 100 | + | 100 | × | 80 100 | x | ( | x | − | 10 | ) |
| 方程左边 = | 90 | x |
| 90 | x | = | 10 | × | 100 | + | 100 | × | 80 100 | x | ( | x | − | 10 | ) |
| 方程右边 = | 1000 | + | 80 | x | ( | x | − | 10 | ) |
| 90 | x | = | 1000 | + | 80 | x | ( | x | − | 10 | ) |
| 方程右边 = | 1000 | + | 80 | x | x | − | 80 | x | × | 10 |
| = | 1000 | + | 80 | x | x | − | 800 | x |
| 90 | x | = | 1000 | + | 80 | x | x | − | 800 | x |