| ( | 2 | x | − | 380 | ) | ( | x | − | 150 | ) | = | 1750 |
| 方程左边 = | 2 | x | ( | x | − | 150 | ) | − | 380 | ( | x | − | 150 | ) |
| = | 2 | x | x | − | 2 | x | × | 150 | − | 380 | ( | x | − | 150 | ) |
| = | 2 | x | x | − | 300 | x | − | 380 | ( | x | − | 150 | ) |
| = | 2 | x | x | − | 300 | x | − | 380 | x | + | 380 | × | 150 |
| = | 2 | x | x | − | 300 | x | − | 380 | x | + | 57000 |
| = | 2 | x | x | − | 680 | x | + | 57000 |
| 2 | x | x | − | 680 | x | + | 57000 | = | 1750 |