| ( | x | − | 50 | ) | × | 5 | ( | 150 | − | x | ) | = | 4000 |
| 方程左边 = | x | × | 5 | ( | 150 | − | x | ) | − | 50 | × | 5 | ( | 150 | − | x | ) |
| = | x | × | 5 | ( | 150 | − | x | ) | − | 250 | ( | 150 | − | x | ) |
| = | x | × | 5 | × | 150 | − | x | × | 5 | x | − | 250 | ( | 150 | − | x | ) |
| = | x | × | 750 | − | x | × | 5 | x | − | 250 | ( | 150 | − | x | ) |
| = | 750 | x | − | x | × | 5 | x | − | 250 | × | 150 | + | 250 | x |
| = | 750 | x | − | x | × | 5 | x | − | 37500 | + | 250 | x |
| = | 1000 | x | − | x | × | 5 | x | − | 37500 |
| 1000 | x | − | x | × | 5 | x | − | 37500 | = | 4000 |