| ( | x | − | 16 | ) | ( | - | 30 | x | + | 960 | ) | = | 1920 |
| 方程左边 = | x | ( | - | 30 | x | + | 960 | ) | − | 16 | ( | - | 30 | x | + | 960 | ) |
| = | - | x | × | 30 | x | + | x | × | 960 | − | 16 | ( | - | 30 | x | + | 960 | ) |
| = | - | x | × | 30 | x | + | 960 | x | + | 16 | × | 30 | x | − | 16 | × | 960 |
| = | - | x | × | 30 | x | + | 960 | x | + | 480 | x | − | 15360 |
| = | - | x | × | 30 | x | + | 1440 | x | − | 15360 |
| - | x | × | 30 | x | + | 1440 | x | − | 15360 | = | 1920 |