| ( | 15000 | − | 500 | x | ) | ( | 1 | − | x | ) | = | 65000 |
| 方程左边 = | 15000 | ( | 1 | − | x | ) | − | 500 | x | ( | 1 | − | x | ) |
| = | 15000 | × | 1 | − | 15000 | x | − | 500 | x | ( | 1 | − | x | ) |
| = | 15000 | − | 15000 | x | − | 500 | x | ( | 1 | − | x | ) |
| = | 15000 | − | 15000 | x | − | 500 | x | × | 1 | + | 500 | x | x |
| = | 15000 | − | 15000 | x | − | 500 | x | + | 500 | x | x |
| = | 15000 | − | 15500 | x | + | 500 | x | x |
| 15000 | − | 15500 | x | + | 500 | x | x | = | 65000 |