| ( | 32 | − | 8 | x | ) | ( | 20 | − | 5 | x | ) | = | 504 |
| 方程左边 = | 32 | ( | 20 | − | 5 | x | ) | − | 8 | x | ( | 20 | − | 5 | x | ) |
| = | 32 | × | 20 | − | 32 | × | 5 | x | − | 8 | x | ( | 20 | − | 5 | x | ) |
| = | 640 | − | 160 | x | − | 8 | x | ( | 20 | − | 5 | x | ) |
| = | 640 | − | 160 | x | − | 8 | x | × | 20 | + | 8 | x | × | 5 | x |
| = | 640 | − | 160 | x | − | 160 | x | + | 40 | x | x |
| = | 640 | − | 320 | x | + | 40 | x | x |
| 640 | − | 320 | x | + | 40 | x | x | = | 504 |