| ( | 2 | + | 1 2 | x | ) | ( | 5000 | − | 10 | x | ) | − | 2 | × | 5000 | − | 400 | x | = | 39600 |
| 方程左边 = | ( | 2 | + | 1 2 | x | ) | ( | 5000 | − | 10 | x | ) | − | 10000 | − | 400 | x |
| ( | 2 | + | 1 2 | x | ) | ( | 5000 | − | 10 | x | ) | − | 10000 | − | 400 | x | = | 39600 |
| 方程左边 = | 2 | ( | 5000 | − | 10 | x | ) | + | 1 2 | x | ( | 5000 | − | 10 | x | ) | − | 10000 | − | 400 | x |
| = | 2 | × | 5000 | − | 2 | × | 10 | x | + | 1 2 | x | ( | 5000 | − | 10 | x | ) | − | 10000 | − | 400 | x |
| = | 10000 | − | 20 | x | + | 1 2 | x | ( | 5000 | − | 10 | x | ) | − | 10000 | − | 400 | x |
| = | 0 | − | 420 | x | + | 1 2 | x | ( | 5000 | − | 10 | x | ) |
| = | - | 420 | x | + | 1 2 | x | × | 5000 | − | 1 2 | x | × | 10 | x |
| = | - | 420 | x | + | 2500 | x | − | 5 | x | x |
| = | 2080 | x | − | 5 | x | x |
| 2080 | x | − | 5 | x | x | = | 39600 |