| ( | x | − | 10 | ) | ( | 80000 | − | 2000 | ( | x | − | 15 | ) | ) | = | 5 | × | 80000 |
| 方程左边 = | x | ( | 80000 | − | 2000 | ( | x | − | 15 | ) | ) | − | 10 | ( | 80000 | − | 2000 | ( | x | − | 15 | ) | ) |
| = | x | × | 80000 | − | x | × | 2000 | ( | x | − | 15 | ) | − | 10 | ( | 80000 | − | 2000 | ( | x | − | 15 | ) | ) |
| = | 80000 | x | − | x | × | 2000 | x | + | x | × | 2000 | × | 15 | − | 10 | ( | 80000 | − | 2000 | ( | x | − | 15 | ) | ) |
| = | 80000 | x | − | x | × | 2000 | x | + | x | × | 30000 | − | 10 | ( | 80000 | − | 2000 | ( | x | − | 15 | ) | ) |
| = | 110000 | x | − | x | × | 2000 | x | − | 10 | ( | 80000 | − | 2000 | ( | x | − | 15 | ) | ) |
| = | 110000 | x | − | x | × | 2000 | x | − | 10 | × | 80000 | + | 10 | × | 2000 | ( | x | − | 15 | ) |
| = | 110000 | x | − | x | × | 2000 | x | − | 800000 | + | 20000 | ( | x | − | 15 | ) |
| = | 110000 | x | − | x | × | 2000 | x | − | 800000 | + | 20000 | x | − | 20000 | × | 15 |
| = | 110000 | x | − | x | × | 2000 | x | − | 800000 | + | 20000 | x | − | 300000 |
| = | 130000 | x | − | x | × | 2000 | x | − | 1100000 |
| 130000 | x | − | x | × | 2000 | x | − | 1100000 | = | 5 | × | 80000 |
| 方程右边 = | 400000 |
| 130000 | x | − | x | × | 2000 | x | − | 1100000 | = | 400000 |