| ( | 40 | − | 18 | − | x | ) | ( | 200000 | + | 20000 | x | ) | = | 3500000 |
| 方程左边 = | 40 | ( | 200000 | + | 20000 | x | ) | − | 18 | ( | 200000 | + | 20000 | x | ) | − | x | ( | 200000 | + | 20000 | x | ) |
| = | 40 | × | 200000 | + | 40 | × | 20000 | x | − | 18 | ( | 200000 | + | 20000 | x | ) | − | x | ( | 200000 | + | 20000 | x | ) |
| = | 8000000 | + | 800000 | x | − | 18 | ( | 200000 | + | 20000 | x | ) | − | x | ( | 200000 | + | 20000 | x | ) |
| = | 8000000 | + | 800000 | x | − | 18 | × | 200000 | − | 18 | × | 20000 | x | − | x | ( | 200000 | + | 20000 | x | ) |
| = | 8000000 | + | 800000 | x | − | 3600000 | − | 360000 | x | − | x | ( | 200000 | + | 20000 | x | ) |
| = | 4400000 | + | 440000 | x | − | x | ( | 200000 | + | 20000 | x | ) |
| = | 4400000 | + | 440000 | x | − | x | × | 200000 | − | x | × | 20000 | x |
| = | 4400000 | + | 240000 | x | − | x | × | 20000 | x |
| 4400000 | + | 240000 | x | − | x | × | 20000 | x | = | 3500000 |