| ( | 100 | − | 5 | x | ) | ( | 60 | − | 3 | x | ) | = | 4860 |
| 方程左边 = | 100 | ( | 60 | − | 3 | x | ) | − | 5 | x | ( | 60 | − | 3 | x | ) |
| = | 100 | × | 60 | − | 100 | × | 3 | x | − | 5 | x | ( | 60 | − | 3 | x | ) |
| = | 6000 | − | 300 | x | − | 5 | x | ( | 60 | − | 3 | x | ) |
| = | 6000 | − | 300 | x | − | 5 | x | × | 60 | + | 5 | x | × | 3 | x |
| = | 6000 | − | 300 | x | − | 300 | x | + | 15 | x | x |
| = | 6000 | − | 600 | x | + | 15 | x | x |
| 6000 | − | 600 | x | + | 15 | x | x | = | 4860 |