| ( | 200 | + | 5 | x | ) | ( | 50 | − | x | ) | = | 10125 |
| 方程左边 = | 200 | ( | 50 | − | x | ) | + | 5 | x | ( | 50 | − | x | ) |
| = | 200 | × | 50 | − | 200 | x | + | 5 | x | ( | 50 | − | x | ) |
| = | 10000 | − | 200 | x | + | 5 | x | ( | 50 | − | x | ) |
| = | 10000 | − | 200 | x | + | 5 | x | × | 50 | − | 5 | x | x |
| = | 10000 | − | 200 | x | + | 250 | x | − | 5 | x | x |
| = | 10000 | + | 50 | x | − | 5 | x | x |
| 10000 | + | 50 | x | − | 5 | x | x | = | 10125 |