| ( | 100 | − | x | − | 40 | ) | ( | 200 | + | 20 | x | ) | − | 2000 | = | 22500 |
| 方程左边 = | 100 | ( | 200 | + | 20 | x | ) | − | x | ( | 200 | + | 20 | x | ) | − | 40 | ( | 200 | + | 20 | x | ) | − | 2000 |
| = | 100 | × | 200 | + | 100 | × | 20 | x | − | x | ( | 200 | + | 20 | x | ) | − | 40 | ( | 200 | + | 20 | x | ) | − | 2000 |
| = | 20000 | + | 2000 | x | − | x | ( | 200 | + | 20 | x | ) | − | 40 | ( | 200 | + | 20 | x | ) | − | 2000 |
| = | 18000 | + | 2000 | x | − | x | ( | 200 | + | 20 | x | ) | − | 40 | ( | 200 | + | 20 | x | ) |
| = | 18000 | + | 2000 | x | − | x | × | 200 | − | x | × | 20 | x | − | 40 | ( | 200 | + | 20 | x | ) |
| = | 18000 | + | 1800 | x | − | x | × | 20 | x | − | 40 | ( | 200 | + | 20 | x | ) |
| = | 18000 | + | 1800 | x | − | x | × | 20 | x | − | 40 | × | 200 | − | 40 | × | 20 | x |
| = | 18000 | + | 1800 | x | − | x | × | 20 | x | − | 8000 | − | 800 | x |
| = | 10000 | + | 1000 | x | − | x | × | 20 | x |
| 10000 | + | 1000 | x | − | x | × | 20 | x | = | 22500 |