| 3 | x | × | 2 | x | × | 100 | + | 30 | ( | 3 | x | × | 2 | x | − | 50 | × | 40 | ) | = | 642000 |
| 方程左边 = | 600 | x | x | + | 30 | ( | 3 | x | × | 2 | x | − | 50 | × | 40 | ) |
| 600 | x | x | + | 30 | ( | 3 | x | × | 2 | x | − | 50 | × | 40 | ) | = | 642000 |
| 方程左边 = | 600 | x | x | + | 30 | × | 3 | x | × | 2 | x | − | 30 | × | 50 | × | 40 |
| = | 600 | x | x | + | 180 | x | x | − | 60000 |
| 600 | x | x | + | 180 | x | x | − | 60000 | = | 642000 |