| ( | x | − | 3 | ) | ( | x | + | 4 | ) | − | ( | - | 12 | ) | = | 0 |
| 方程左边 = | x | ( | x | + | 4 | ) | − | 3 | ( | x | + | 4 | ) | − | ( | - | 12 | ) |
| = | x | x | + | x | × | 4 | − | 3 | ( | x | + | 4 | ) | − | ( | - | 12 | ) |
| = | x | x | + | 4 | x | − | 3 | x | − | 3 | × | 4 | − | ( | - | 12 | ) |
| = | x | x | + | 4 | x | − | 3 | x | − | 12 | − | ( | - | 12 | ) |
| = | x | x | + | 1 | x | − | 12 | − | ( | - | 12 | ) |
| = | x | x | + | 1 | x | − | 12 | + | 12 |
| = | x | x | + | 1 | x | − | 0 |
| x | x | + | 1 | x | = | 0 |