| ( | 60 | + | x | ) | ( | 120 | − | 1 2 | x | ) | = | 10000 |
| 方程左边 = | 60 | ( | 120 | − | 1 2 | x | ) | + | x | ( | 120 | − | 1 2 | x | ) |
| = | 60 | × | 120 | − | 60 | × | 1 2 | x | + | x | ( | 120 | − | 1 2 | x | ) |
| = | 7200 | − | 30 | x | + | x | ( | 120 | − | 1 2 | x | ) |
| = | 7200 | − | 30 | x | + | x | × | 120 | − | x | × | 1 2 | x |
| = | 7200 | + | 90 | x | − | x | × | 1 2 | x |
| 7200 | + | 90 | x | − | x | × | 1 2 | x | = | 10000 |