| ( | 60 | − | x | ) | ( | 30 | + | 3 | x | ) | = | 2 | × | 60 | × | 30 |
| 方程左边 = | 60 | ( | 30 | + | 3 | x | ) | − | x | ( | 30 | + | 3 | x | ) |
| = | 60 | × | 30 | + | 60 | × | 3 | x | − | x | ( | 30 | + | 3 | x | ) |
| = | 1800 | + | 180 | x | − | x | ( | 30 | + | 3 | x | ) |
| = | 1800 | + | 180 | x | − | x | × | 30 | − | x | × | 3 | x |
| = | 1800 | + | 150 | x | − | x | × | 3 | x |
| 1800 | + | 150 | x | − | x | × | 3 | x | = | 2 | × | 60 | × | 30 |
| 方程右边 = | 3600 |
| 1800 | + | 150 | x | − | x | × | 3 | x | = | 3600 |