| 400 | × | 400 | + | ( | 5000 | − | x | ) | ( | 5000 | − | x | ) | = | 5000 | × | 5000 |
| 方程左边 = | 160000 | + | ( | 5000 | − | x | ) | ( | 5000 | − | x | ) |
| 160000 | + | ( | 5000 | − | x | ) | ( | 5000 | − | x | ) | = | 5000 | × | 5000 |
| 方程左边 = | 160000 | + | 5000 | ( | 5000 | − | x | ) | − | x | ( | 5000 | − | x | ) |
| = | 160000 | + | 5000 | × | 5000 | − | 5000 | x | − | x | ( | 5000 | − | x | ) |
| = | 160000 | + | 25000000 | − | 5000 | x | − | x | ( | 5000 | − | x | ) |
| = | 25160000 | − | 5000 | x | − | x | ( | 5000 | − | x | ) |
| = | 25160000 | − | 5000 | x | − | x | × | 5000 | + | x | x |
| = | 25160000 | − | 10000 | x | + | x | x |
| 25160000 | − | 10000 | x | + | x | x | = | 5000 | × | 5000 |
| 方程右边 = | 25000000 |
| 25160000 | − | 10000 | x | + | x | x | = | 25000000 |