| 3 | ( | x | + | 4 | ) | ( | x | + | 4 | ) | = | x | x | − | 16 |
| 方程左边 = | 3 | x | ( | x | + | 4 | ) | + | 3 | × | 4 | ( | x | + | 4 | ) |
| = | 3 | x | ( | x | + | 4 | ) | + | 12 | ( | x | + | 4 | ) |
| = | 3 | x | x | + | 3 | x | × | 4 | + | 12 | ( | x | + | 4 | ) |
| = | 3 | x | x | + | 12 | x | + | 12 | ( | x | + | 4 | ) |
| = | 3 | x | x | + | 12 | x | + | 12 | x | + | 12 | × | 4 |
| = | 3 | x | x | + | 12 | x | + | 12 | x | + | 48 |
| = | 3 | x | x | + | 24 | x | + | 48 |
| 3 | x | x | + | 24 | x | + | 48 | = | x | x | − | 16 |