| ( | 500 | − | ( | x | − | 50 | ) | x | × | 10 | ) | ( | x | − | 40 | ) | = | 8750 |
| 方程左边 = | 500 | ( | x | − | 40 | ) | − | ( | x | − | 50 | ) | x | × | 10 | ( | x | − | 40 | ) |
| = | 500 | x | − | 500 | × | 40 | − | ( | x | − | 50 | ) | x | × | 10 | ( | x | − | 40 | ) |
| = | 500 | x | − | 20000 | − | ( | x | − | 50 | ) | x | × | 10 | ( | x | − | 40 | ) |
| = | 500 | x | − | 20000 | − | x | x | × | 10 | ( | x | − | 40 | ) | + | 50 | x | × | 10 | ( | x | − | 40 | ) |
| = | 500 | x | − | 20000 | − | x | x | × | 10 | ( | x | − | 40 | ) | + | 500 | x | ( | x | − | 40 | ) |
| = | 500 | x | − | 20000 | − | x | x | × | 10 | x | + | x | x | × | 10 | × | 40 | + | 500 |
| = | 500 | x | − | 20000 | − | x | x | × | 10 | x | + | x | x | × | 400 | + | 500 | x |
| = | 500 | x | − | 20000 | − | x | x | × | 10 | x | + | x | x | × | 400 | + | 500 | x |
| = | 500 | x | − | 20000 | − | x | x | × | 10 | x | + | x | x | × | 400 | + | 500 | x |
| = | - | 19500 | x | − | 20000 | − | x | x | × | 10 | x | + | x | x | × | 400 | + | 500 | x |
| - | 19500 | x | − | 20000 | − | x | x | × | 10 | x | + | x | x | × | 400 | + | 500 | x | = | 8750 |