| ( | 80000 | − | 2000 | x | ) | ( | 5 2 | − | 1 10 | x | ) | − | 200000 | = | 0 |
| 方程左边 = | 80000 | ( | 5 2 | − | 1 10 | x | ) | − | 2000 | x | ( | 5 2 | − | 1 10 | x | ) | − | 200000 |
| = | 80000 | × | 5 2 | − | 80000 | × | 1 10 | x | − | 2000 | x | ( | 5 2 | − | 1 10 | x | ) | − | 200000 |
| = | 200000 | − | 8000 | x | − | 2000 | x | ( | 5 2 | − | 1 10 | x | ) | − | 200000 |
| = | 0 | − | 8000 | x | − | 2000 | x | ( | 5 2 | − | 1 10 | x | ) |
| = | - | 8000 | x | − | 2000 | x | × | 5 2 | + | 2000 | x | × | 1 10 | x |
| = | - | 8000 | x | − | 5000 | x | + | 200 | x | x |
| = | - | 13000 | x | + | 200 | x | x |
| - | 13000 | x | + | 200 | x | x | = | 0 |