| ( | 20 | ( | 60 | − | x | ) | + | 300 | ) | ( | x | − | 40 | ) | = | 6080 |
| 方程左边 = | 20 | ( | 60 | − | x | ) | ( | x | − | 40 | ) | + | 300 | ( | x | − | 40 | ) |
| = | 20 | × | 60 | ( | x | − | 40 | ) | − | 20 | x | ( | x | − | 40 | ) | + | 300 | ( | x | − | 40 | ) |
| = | 1200 | ( | x | − | 40 | ) | − | 20 | x | ( | x | − | 40 | ) | + | 300 | ( | x | − | 40 | ) |
| = | 1200 | x | − | 1200 | × | 40 | − | 20 | x | ( | x | − | 40 | ) | + | 300 | ( | x | − | 40 | ) |
| = | 1200 | x | − | 48000 | − | 20 | x | ( | x | − | 40 | ) | + | 300 | ( | x | − | 40 | ) |
| = | 1200 | x | − | 48000 | − | 20 | x | x | + | 20 | x | × | 40 | + | 300 | ( | x | − | 40 | ) |
| = | 1200 | x | − | 48000 | − | 20 | x | x | + | 800 | x | + | 300 | ( | x | − | 40 | ) |
| = | 2000 | x | − | 48000 | − | 20 | x | x | + | 300 | ( | x | − | 40 | ) |
| = | 2000 | x | − | 48000 | − | 20 | x | x | + | 300 | x | − | 300 | × | 40 |
| = | 2000 | x | − | 48000 | − | 20 | x | x | + | 300 | x | − | 12000 |
| = | 2300 | x | − | 60000 | − | 20 | x | x |
| 2300 | x | − | 60000 | − | 20 | x | x | = | 6080 |