| ( | 40 | − | 2 | x | ) | ( | 1000 | − | 4 | x | − | 200 | ) | = | 15200 |
| 方程左边 = | 40 | ( | 1000 | − | 4 | x | − | 200 | ) | − | 2 | x | ( | 1000 | − | 4 | x | − | 200 | ) |
| = | 40 | × | 1000 | − | 40 | × | 4 | x | − | 40 | × | 200 | − | 2 | x | ( | 1000 | − | 4 | x | − | 200 | ) |
| = | 40000 | − | 160 | x | − | 8000 | − | 2 | x | ( | 1000 | − | 4 | x | − | 200 | ) |
| = | 32000 | − | 160 | x | − | 2 | x | ( | 1000 | − | 4 | x | − | 200 | ) |
| = | 32000 | − | 160 | x | − | 2 | x | × | 1000 | + | 2 | x | × | 4 | x | + | 2 | x |
| = | 32000 | − | 160 | x | − | 2000 | x | + | 8 | x | x | + | 400 | x |
| = | 32000 | − | 1760 | x | + | 8 | x | x |
| 32000 | − | 1760 | x | + | 8 | x | x | = | 15200 |