| ( | x | + | 3 | ) | ( | x | + | 12 | ) | = | 2 | x | ( | x | + | 6 | ) | − | 4 |
| 方程左边 = | x | ( | x | + | 12 | ) | + | 3 | ( | x | + | 12 | ) |
| = | x | x | + | x | × | 12 | + | 3 | ( | x | + | 12 | ) |
| = | x | x | + | 12 | x | + | 3 | x | + | 3 | × | 12 |
| = | x | x | + | 12 | x | + | 3 | x | + | 36 |
| = | x | x | + | 15 | x | + | 36 |
| x | x | + | 15 | x | + | 36 | = | 2 | x | ( | x | + | 6 | ) | − | 4 |
| 方程右边 = | 2 | x | x | + | 2 | x | × | 6 | − | 4 |
| = | 2 | x | x | + | 12 | x | − | 4 |
| x | x | + | 15 | x | + | 36 | = | 2 | x | x | + | 12 | x | − | 4 |