| 60 | × | 40 | − | ( | 60 | − | 2 | x | ) | ( | 40 | − | x | ) | = | 650 |
| 方程左边 = | 2400 | − | ( | 60 | − | 2 | x | ) | ( | 40 | − | x | ) |
| 2400 | − | ( | 60 | − | 2 | x | ) | ( | 40 | − | x | ) | = | 650 |
| 方程左边 = | 2400 | − | 60 | ( | 40 | − | x | ) | + | 2 | x | ( | 40 | − | x | ) |
| = | 2400 | − | 60 | × | 40 | + | 60 | x | + | 2 | x | ( | 40 | − | x | ) |
| = | 2400 | − | 2400 | + | 60 | x | + | 2 | x | ( | 40 | − | x | ) |
| = | 0 | + | 60 | x | + | 2 | x | ( | 40 | − | x | ) |
| = | 60 | x | + | 2 | x | × | 40 | − | 2 | x | x |
| = | 60 | x | + | 80 | x | − | 2 | x | x |
| = | 140 | x | − | 2 | x | x |
| 140 | x | − | 2 | x | x | = | 650 |