| ( | 100 | − | 2 | ( | x | − | 50 | ) | ) | ( | x | − | 40 | ) | = | 1350 |
| 方程左边 = | 100 | ( | x | − | 40 | ) | − | 2 | ( | x | − | 50 | ) | ( | x | − | 40 | ) |
| = | 100 | x | − | 100 | × | 40 | − | 2 | ( | x | − | 50 | ) | ( | x | − | 40 | ) |
| = | 100 | x | − | 4000 | − | 2 | ( | x | − | 50 | ) | ( | x | − | 40 | ) |
| = | 100 | x | − | 4000 | − | 2 | x | ( | x | − | 40 | ) | + | 2 | × | 50 | ( | x | − | 40 | ) |
| = | 100 | x | − | 4000 | − | 2 | x | ( | x | − | 40 | ) | + | 100 | ( | x | − | 40 | ) |
| = | 100 | x | − | 4000 | − | 2 | x | x | + | 2 | x | × | 40 | + | 100 | ( | x | − | 40 | ) |
| = | 100 | x | − | 4000 | − | 2 | x | x | + | 80 | x | + | 100 | ( | x | − | 40 | ) |
| = | 180 | x | − | 4000 | − | 2 | x | x | + | 100 | ( | x | − | 40 | ) |
| = | 180 | x | − | 4000 | − | 2 | x | x | + | 100 | x | − | 100 | × | 40 |
| = | 180 | x | − | 4000 | − | 2 | x | x | + | 100 | x | − | 4000 |
| = | 280 | x | − | 8000 | − | 2 | x | x |
| 280 | x | − | 8000 | − | 2 | x | x | = | 1350 |