| 80000 | − | ( | 100 | + | x | ) | ( | 1000 | − | 5 | x | ) | = | 60500 |
| 方程左边 = | 80000 | − | 100 | ( | 1000 | − | 5 | x | ) | − | x | ( | 1000 | − | 5 | x | ) |
| = | 80000 | − | 100 | × | 1000 | + | 100 | × | 5 | x | − | x | ( | 1000 | − | 5 | x | ) |
| = | 80000 | − | 100000 | + | 500 | x | − | x | ( | 1000 | − | 5 | x | ) |
| = | - | 20000 | + | 500 | x | − | x | ( | 1000 | − | 5 | x | ) |
| = | - | 20000 | + | 500 | x | − | x | × | 1000 | + | x | × | 5 | x |
| = | - | 20000 | − | 500 | x | + | x | × | 5 | x |
| - | 20000 | − | 500 | x | + | x | × | 5 | x | = | 60500 |