| ( | 2 | x | − | 30 | ) | × | 100 | = | ( | x | − | 100 | ) | ( | x | − | 30 | ) |
| 方程左边 = | 2 | x | × | 100 | − | 30 | × | 100 |
| = | 200 | x | − | 3000 |
| 200 | x | − | 3000 | = | ( | x | − | 100 | ) | ( | x | − | 30 | ) |
| 方程右边 = | x | ( | x | − | 30 | ) | − | 100 | ( | x | − | 30 | ) |
| = | x | x | − | x | × | 30 | − | 100 | ( | x | − | 30 | ) |
| = | x | x | − | 30 | x | − | 100 | x | + | 100 | × | 30 |
| = | x | x | − | 30 | x | − | 100 | x | + | 3000 |
| = | x | x | − | 130 | x | + | 3000 |
| 200 | x | − | 3000 | = | x | x | − | 130 | x | + | 3000 |