| 160 | ( | x | + | 40 | ) | = | ( | x | − | 160 | ) | ( | x | − | 280 | ) |
| 方程左边 = | 160 | x | + | 160 | × | 40 |
| = | 160 | x | + | 6400 |
| 160 | x | + | 6400 | = | ( | x | − | 160 | ) | ( | x | − | 280 | ) |
| 方程右边 = | x | ( | x | − | 280 | ) | − | 160 | ( | x | − | 280 | ) |
| = | x | x | − | x | × | 280 | − | 160 | ( | x | − | 280 | ) |
| = | x | x | − | 280 | x | − | 160 | x | + | 160 | × | 280 |
| = | x | x | − | 280 | x | − | 160 | x | + | 44800 |
| = | x | x | − | 440 | x | + | 44800 |
| 160 | x | + | 6400 | = | x | x | − | 440 | x | + | 44800 |