| ( | x | + | 3 | ) | ( | x | − | 9 | ) | = | ( | x | + | 6 | ) | ( | x | + | 7 | ) |
| 方程左边 = | x | ( | x | − | 9 | ) | + | 3 | ( | x | − | 9 | ) |
| = | x | x | − | x | × | 9 | + | 3 | ( | x | − | 9 | ) |
| = | x | x | − | 9 | x | + | 3 | x | − | 3 | × | 9 |
| = | x | x | − | 9 | x | + | 3 | x | − | 27 |
| = | x | x | − | 6 | x | − | 27 |
| x | x | − | 6 | x | − | 27 | = | ( | x | + | 6 | ) | ( | x | + | 7 | ) |
| 方程右边 = | x | ( | x | + | 7 | ) | + | 6 | ( | x | + | 7 | ) |
| = | x | x | + | x | × | 7 | + | 6 | ( | x | + | 7 | ) |
| = | x | x | + | 7 | x | + | 6 | x | + | 6 | × | 7 |
| = | x | x | + | 7 | x | + | 6 | x | + | 42 |
| = | x | x | + | 13 | x | + | 42 |
| x | x | − | 6 | x | − | 27 | = | x | x | + | 13 | x | + | 42 |