| ( | 80 | − | 2 | x | ) | x | ( | 1200 | + | 200 | x | ) | − | 64000 | = | 122000 |
| 方程左边 = | 80 | x | ( | 1200 | + | 200 | x | ) | − | 2 | x | x | ( | 1200 | + | 200 | x | ) | − | 64000 |
| = | 80 | x | × | 1200 | + | 80 | x | × | 200 | x | − | 2 | x | x | ( | 1200 | + | 200 | x | ) | − | 64000 |
| = | 96000 | x | + | 16000 | x | x | − | 2 | x | x | ( | 1200 | + | 200 | x | ) | − | 64000 |
| = | 96000 | x | + | 16000 | x | x | − | 2 | x | x | × | 1200 | − | 2 | x | x |
| = | 96000 | x | + | 16000 | x | x | − | 2400 | x | x | − | 400 | x | x | x |
| 96000 | x | + | 16000 | x | x | − | 2400 | x | x | − | 400 | x | x | x | = | 122000 |