| ( | 40 | x | + | 400 | ) | ( | 14 | − | 8 | − | x | ) | = | 1920 |
| 方程左边 = | 40 | x | ( | 14 | − | 8 | − | x | ) | + | 400 | ( | 14 | − | 8 | − | x | ) |
| = | 40 | x | × | 14 | − | 40 | x | × | 8 | − | 40 | x | x | + | 400 | ( | 14 | − | 8 | − | x | ) |
| = | 560 | x | − | 320 | x | − | 40 | x | x | + | 400 | ( | 14 | − | 8 | − | x | ) |
| = | 240 | x | − | 40 | x | x | + | 400 | ( | 14 | − | 8 | − | x | ) |
| = | 240 | x | − | 40 | x | x | + | 400 | × | 14 | − | 400 | × | 8 | − | 400 | x |
| = | 240 | x | − | 40 | x | x | + | 5600 | − | 3200 | − | 400 | x |
| = | - | 160 | x | − | 40 | x | x | + | 2400 |
| - | 160 | x | − | 40 | x | x | + | 2400 | = | 1920 |