| ( | x | + | 50 | ) | ( | 600 | − | 50 | x | ) | = | 15000 |
| 方程左边 = | x | ( | 600 | − | 50 | x | ) | + | 50 | ( | 600 | − | 50 | x | ) |
| = | x | × | 600 | − | x | × | 50 | x | + | 50 | ( | 600 | − | 50 | x | ) |
| = | 600 | x | − | x | × | 50 | x | + | 50 | × | 600 | − | 50 | × | 50 | x |
| = | 600 | x | − | x | × | 50 | x | + | 30000 | − | 2500 | x |
| = | - | 1900 | x | − | x | × | 50 | x | + | 30000 |
| - | 1900 | x | − | x | × | 50 | x | + | 30000 | = | 15000 |