| ( | 60 | − | 600 | + | 10 | x | ) | ( | x | − | 40 | ) | = | 400 |
| 方程左边 = | 60 | ( | x | − | 40 | ) | − | 600 | ( | x | − | 40 | ) | + | 10 | x | ( | x | − | 40 | ) |
| = | 60 | x | − | 60 | × | 40 | − | 600 | ( | x | − | 40 | ) | + | 10 | x | ( | x | − | 40 | ) |
| = | 60 | x | − | 2400 | − | 600 | ( | x | − | 40 | ) | + | 10 | x | ( | x | − | 40 | ) |
| = | 60 | x | − | 2400 | − | 600 | x | + | 600 | × | 40 | + | 10 | x | ( | x | − | 40 | ) |
| = | 60 | x | − | 2400 | − | 600 | x | + | 24000 | + | 10 | x | ( | x | − | 40 | ) |
| = | - | 540 | x | + | 21600 | + | 10 | x | ( | x | − | 40 | ) |
| = | - | 540 | x | + | 21600 | + | 10 | x | x | − | 10 | x | × | 40 |
| = | - | 540 | x | + | 21600 | + | 10 | x | x | − | 400 | x |
| = | - | 940 | x | + | 21600 | + | 10 | x | x |
| - | 940 | x | + | 21600 | + | 10 | x | x | = | 400 |